Stop vendoring toml11

We don't apply any patches to it, and vendoring it locks users into
bugs (it hasn't been updated since its introduction in late 2021).

Closes https://git.lix.systems/lix-project/lix/issues/164

Change-Id: Ied071c841fc30b0dfb575151afd1e7f66970fdb9

22 files changed, 0 insertions, 10825 deletions

diff --git a/src/toml11/toml/color.hpp b/src/toml11/toml/color.hpp
deleted file mode 100644
index 4cb572cb0..000000000
--- a/src/toml11/toml/color.hpp
+++ /dev/null
@@ -1,64 +0,0 @@
-#ifndef TOML11_COLOR_HPP
-#define TOML11_COLOR_HPP
-#include <cstdint>
-#include <ostream>
-
-#ifdef TOML11_COLORIZE_ERROR_MESSAGE
-#define TOML11_ERROR_MESSAGE_COLORIZED true
-#else
-#define TOML11_ERROR_MESSAGE_COLORIZED false
-#endif
-
-namespace toml
-{
-
-// put ANSI escape sequence to ostream
-namespace color_ansi
-{
-namespace detail
-{
-inline int colorize_index()
-{
-    static const int index = std::ios_base::xalloc();
-    return index;
-}
-} // detail
-
-inline std::ostream& colorize(std::ostream& os)
-{
-    // by default, it is zero.
-    os.iword(detail::colorize_index()) = 1;
-    return os;
-}
-inline std::ostream& nocolorize(std::ostream& os)
-{
-    os.iword(detail::colorize_index()) = 0;
-    return os;
-}
-inline std::ostream& reset  (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[00m";} return os;}
-inline std::ostream& bold   (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[01m";} return os;}
-inline std::ostream& grey   (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[30m";} return os;}
-inline std::ostream& red    (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[31m";} return os;}
-inline std::ostream& green  (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[32m";} return os;}
-inline std::ostream& yellow (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[33m";} return os;}
-inline std::ostream& blue   (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[34m";} return os;}
-inline std::ostream& magenta(std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[35m";} return os;}
-inline std::ostream& cyan   (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[36m";} return os;}
-inline std::ostream& white  (std::ostream& os)
-{if(os.iword(detail::colorize_index()) == 1) {os << "\033[37m";} return os;}
-} // color_ansi
-
-// ANSI escape sequence is the only and default colorization method currently
-namespace color = color_ansi;
-
-} // toml
-#endif// TOML11_COLOR_HPP
diff --git a/src/toml11/toml/combinator.hpp b/src/toml11/toml/combinator.hpp
deleted file mode 100644
index 33ecca1eb..000000000
--- a/src/toml11/toml/combinator.hpp
+++ /dev/null
@@ -1,306 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_COMBINATOR_HPP
-#define TOML11_COMBINATOR_HPP
-#include <cassert>
-#include <cctype>
-#include <cstdio>
-
-#include <array>
-#include <iomanip>
-#include <iterator>
-#include <limits>
-#include <type_traits>
-
-#include "region.hpp"
-#include "result.hpp"
-#include "traits.hpp"
-#include "utility.hpp"
-
-// they scans characters and returns region if it matches to the condition.
-// when they fail, it does not change the location.
-// in lexer.hpp, these are used.
-
-namespace toml
-{
-namespace detail
-{
-
-// to output character as an error message.
-inline std::string show_char(const char c)
-{
-    // It suppresses an error that occurs only in Debug mode of MSVC++ on Windows.
-    // I'm not completely sure but they check the value of char to be in the
-    // range [0, 256) and some of the COMPLETELY VALID utf-8 character sometimes
-    // has negative value (if char has sign). So here it re-interprets c as
-    // unsigned char through pointer. In general, converting pointer to a
-    // pointer that has different type cause UB, but `(signed|unsigned)?char`
-    // are one of the exceptions. Converting pointer only to char and std::byte
-    // (c++17) are valid.
-    if(std::isgraph(*reinterpret_cast<unsigned char const*>(std::addressof(c))))
-    {
-        return std::string(1, c);
-    }
-    else
-    {
-        std::array<char, 5> buf;
-        buf.fill('\0');
-        const auto r = std::snprintf(
-                buf.data(), buf.size(), "0x%02x", static_cast<int>(c) & 0xFF);
-        (void) r; // Unused variable warning
-        assert(r == static_cast<int>(buf.size()) - 1);
-        return std::string(buf.data());
-    }
-}
-
-template<char C>
-struct character
-{
-    static constexpr char target = C;
-
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        if(loc.iter() == loc.end()) {return none();}
-        const auto first = loc.iter();
-
-        const char c = *(loc.iter());
-        if(c != target)
-        {
-            return none();
-        }
-        loc.advance(); // update location
-
-        return ok(region(loc, first, loc.iter()));
-    }
-};
-template<char C>
-constexpr char character<C>::target;
-
-// closed interval [Low, Up]. both Low and Up are included.
-template<char Low, char Up>
-struct in_range
-{
-    // assuming ascii part of UTF-8...
-    static_assert(Low <= Up, "lower bound should be less than upper bound.");
-
-    static constexpr char upper = Up;
-    static constexpr char lower = Low;
-
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        if(loc.iter() == loc.end()) {return none();}
-        const auto first = loc.iter();
-
-        const char c = *(loc.iter());
-        if(c < lower || upper < c)
-        {
-            return none();
-        }
-
-        loc.advance();
-        return ok(region(loc, first, loc.iter()));
-    }
-};
-template<char L, char U> constexpr char in_range<L, U>::upper;
-template<char L, char U> constexpr char in_range<L, U>::lower;
-
-// keep iterator if `Combinator` matches. otherwise, increment `iter` by 1 char.
-// for detecting invalid characters, like control sequences in toml string.
-template<typename Combinator>
-struct exclude
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        if(loc.iter() == loc.end()) {return none();}
-        auto first = loc.iter();
-
-        auto rslt = Combinator::invoke(loc);
-        if(rslt.is_ok())
-        {
-            loc.reset(first);
-            return none();
-        }
-        loc.reset(std::next(first)); // XXX maybe loc.advance() is okay but...
-        return ok(region(loc, first, loc.iter()));
-    }
-};
-
-// increment `iter`, if matches. otherwise, just return empty string.
-template<typename Combinator>
-struct maybe
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        const auto rslt = Combinator::invoke(loc);
-        if(rslt.is_ok())
-        {
-            return rslt;
-        }
-        return ok(region(loc));
-    }
-};
-
-template<typename ... Ts>
-struct sequence;
-
-template<typename Head, typename ... Tail>
-struct sequence<Head, Tail...>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        const auto first = loc.iter();
-        auto rslt = Head::invoke(loc);
-        if(rslt.is_err())
-        {
-            loc.reset(first);
-            return none();
-        }
-        return sequence<Tail...>::invoke(loc, std::move(rslt.unwrap()), first);
-    }
-
-    // called from the above function only, recursively.
-    template<typename Iterator>
-    static result<region, none_t>
-    invoke(location& loc, region reg, Iterator first)
-    {
-        const auto rslt = Head::invoke(loc);
-        if(rslt.is_err())
-        {
-            loc.reset(first);
-            return none();
-        }
-        reg += rslt.unwrap(); // concat regions
-        return sequence<Tail...>::invoke(loc, std::move(reg), first);
-    }
-};
-
-template<typename Head>
-struct sequence<Head>
-{
-    // would be called from sequence<T ...>::invoke only.
-    template<typename Iterator>
-    static result<region, none_t>
-    invoke(location& loc, region reg, Iterator first)
-    {
-        const auto rslt = Head::invoke(loc);
-        if(rslt.is_err())
-        {
-            loc.reset(first);
-            return none();
-        }
-        reg += rslt.unwrap(); // concat regions
-        return ok(reg);
-    }
-};
-
-template<typename ... Ts>
-struct either;
-
-template<typename Head, typename ... Tail>
-struct either<Head, Tail...>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        const auto rslt = Head::invoke(loc);
-        if(rslt.is_ok()) {return rslt;}
-        return either<Tail...>::invoke(loc);
-    }
-};
-template<typename Head>
-struct either<Head>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        return Head::invoke(loc);
-    }
-};
-
-template<typename T, typename N>
-struct repeat;
-
-template<std::size_t N> struct exactly{};
-template<std::size_t N> struct at_least{};
-struct unlimited{};
-
-template<typename T, std::size_t N>
-struct repeat<T, exactly<N>>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        region retval(loc);
-        const auto first = loc.iter();
-        for(std::size_t i=0; i<N; ++i)
-        {
-            auto rslt = T::invoke(loc);
-            if(rslt.is_err())
-            {
-                loc.reset(first);
-                return none();
-            }
-            retval += rslt.unwrap();
-        }
-        return ok(std::move(retval));
-    }
-};
-
-template<typename T, std::size_t N>
-struct repeat<T, at_least<N>>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        region retval(loc);
-
-        const auto first = loc.iter();
-        for(std::size_t i=0; i<N; ++i)
-        {
-            auto rslt = T::invoke(loc);
-            if(rslt.is_err())
-            {
-                loc.reset(first);
-                return none();
-            }
-            retval += rslt.unwrap();
-        }
-        while(true)
-        {
-            auto rslt = T::invoke(loc);
-            if(rslt.is_err())
-            {
-                return ok(std::move(retval));
-            }
-            retval += rslt.unwrap();
-        }
-    }
-};
-
-template<typename T>
-struct repeat<T, unlimited>
-{
-    static result<region, none_t>
-    invoke(location& loc)
-    {
-        region retval(loc);
-        while(true)
-        {
-            auto rslt = T::invoke(loc);
-            if(rslt.is_err())
-            {
-                return ok(std::move(retval));
-            }
-            retval += rslt.unwrap();
-        }
-    }
-};
-
-} // detail
-} // toml
-#endif// TOML11_COMBINATOR_HPP
diff --git a/src/toml11/toml/comments.hpp b/src/toml11/toml/comments.hpp
deleted file mode 100644
index ec2504117..000000000
--- a/src/toml11/toml/comments.hpp
+++ /dev/null
@@ -1,472 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_COMMENTS_HPP
-#define TOML11_COMMENTS_HPP
-#include <initializer_list>
-#include <iterator>
-#include <stdexcept>
-#include <string>
-#include <type_traits>
-#include <utility>
-#include <vector>
-
-#ifdef TOML11_PRESERVE_COMMENTS_BY_DEFAULT
-#  define TOML11_DEFAULT_COMMENT_STRATEGY ::toml::preserve_comments
-#else
-#  define TOML11_DEFAULT_COMMENT_STRATEGY ::toml::discard_comments
-#endif
-
-// This file provides mainly two classes, `preserve_comments` and `discard_comments`.
-// Those two are a container that have the same interface as `std::vector<std::string>`
-// but bahaves in the opposite way. `preserve_comments` is just the same as
-// `std::vector<std::string>` and each `std::string` corresponds to a comment line.
-// Conversely, `discard_comments` discards all the strings and ignores everything
-// assigned in it. `discard_comments` is always empty and you will encounter an
-// error whenever you access to the element.
-namespace toml
-{
-struct discard_comments; // forward decl
-
-// use it in the following way
-//
-// const toml::basic_value<toml::preserve_comments> data =
-//     toml::parse<toml::preserve_comments>("example.toml");
-//
-// the interface is almost the same as std::vector<std::string>.
-struct preserve_comments
-{
-    // `container_type` is not provided in discard_comments.
-    // do not use this inner-type in a generic code.
-    using container_type         = std::vector<std::string>;
-
-    using size_type              = container_type::size_type;
-    using difference_type        = container_type::difference_type;
-    using value_type             = container_type::value_type;
-    using reference              = container_type::reference;
-    using const_reference        = container_type::const_reference;
-    using pointer                = container_type::pointer;
-    using const_pointer          = container_type::const_pointer;
-    using iterator               = container_type::iterator;
-    using const_iterator         = container_type::const_iterator;
-    using reverse_iterator       = container_type::reverse_iterator;
-    using const_reverse_iterator = container_type::const_reverse_iterator;
-
-    preserve_comments()  = default;
-    ~preserve_comments() = default;
-    preserve_comments(preserve_comments const&) = default;
-    preserve_comments(preserve_comments &&)     = default;
-    preserve_comments& operator=(preserve_comments const&) = default;
-    preserve_comments& operator=(preserve_comments &&)     = default;
-
-    explicit preserve_comments(const std::vector<std::string>& c): comments(c){}
-    explicit preserve_comments(std::vector<std::string>&& c)
-        : comments(std::move(c))
-    {}
-    preserve_comments& operator=(const std::vector<std::string>& c)
-    {
-        comments = c;
-        return *this;
-    }
-    preserve_comments& operator=(std::vector<std::string>&& c)
-    {
-        comments = std::move(c);
-        return *this;
-    }
-
-    explicit preserve_comments(const discard_comments&) {}
-
-    explicit preserve_comments(size_type n): comments(n) {}
-    preserve_comments(size_type n, const std::string& x): comments(n, x) {}
-    preserve_comments(std::initializer_list<std::string> x): comments(x) {}
-    template<typename InputIterator>
-    preserve_comments(InputIterator first, InputIterator last)
-        : comments(first, last)
-    {}
-
-    template<typename InputIterator>
-    void assign(InputIterator first, InputIterator last) {comments.assign(first, last);}
-    void assign(std::initializer_list<std::string> ini)  {comments.assign(ini);}
-    void assign(size_type n, const std::string& val)     {comments.assign(n, val);}
-
-    // Related to the issue #97.
-    //
-    // It is known that `std::vector::insert` and `std::vector::erase` in
-    // the standard library implementation included in GCC 4.8.5 takes
-    // `std::vector::iterator` instead of `std::vector::const_iterator`.
-    // Because of the const-correctness, we cannot convert a `const_iterator` to
-    // an `iterator`. It causes compilation error in GCC 4.8.5.
-#if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__) && !defined(__clang__)
-#  if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) <= 40805
-#    define TOML11_WORKAROUND_GCC_4_8_X_STANDARD_LIBRARY_IMPLEMENTATION
-#  endif
-#endif
-
-#ifdef TOML11_WORKAROUND_GCC_4_8_X_STANDARD_LIBRARY_IMPLEMENTATION
-    iterator insert(iterator p, const std::string& x)
-    {
-        return comments.insert(p, x);
-    }
-    iterator insert(iterator p, std::string&&      x)
-    {
-        return comments.insert(p, std::move(x));
-    }
-    void insert(iterator p, size_type n, const std::string& x)
-    {
-        return comments.insert(p, n, x);
-    }
-    template<typename InputIterator>
-    void insert(iterator p, InputIterator first, InputIterator last)
-    {
-        return comments.insert(p, first, last);
-    }
-    void insert(iterator p, std::initializer_list<std::string> ini)
-    {
-        return comments.insert(p, ini);
-    }
-
-    template<typename ... Ts>
-    iterator emplace(iterator p, Ts&& ... args)
-    {
-        return comments.emplace(p, std::forward<Ts>(args)...);
-    }
-
-    iterator erase(iterator pos) {return comments.erase(pos);}
-    iterator erase(iterator first, iterator last)
-    {
-        return comments.erase(first, last);
-    }
-#else
-    iterator insert(const_iterator p, const std::string& x)
-    {
-        return comments.insert(p, x);
-    }
-    iterator insert(const_iterator p, std::string&&      x)
-    {
-        return comments.insert(p, std::move(x));
-    }
-    iterator insert(const_iterator p, size_type n, const std::string& x)
-    {
-        return comments.insert(p, n, x);
-    }
-    template<typename InputIterator>
-    iterator insert(const_iterator p, InputIterator first, InputIterator last)
-    {
-        return comments.insert(p, first, last);
-    }
-    iterator insert(const_iterator p, std::initializer_list<std::string> ini)
-    {
-        return comments.insert(p, ini);
-    }
-
-    template<typename ... Ts>
-    iterator emplace(const_iterator p, Ts&& ... args)
-    {
-        return comments.emplace(p, std::forward<Ts>(args)...);
-    }
-
-    iterator erase(const_iterator pos) {return comments.erase(pos);}
-    iterator erase(const_iterator first, const_iterator last)
-    {
-        return comments.erase(first, last);
-    }
-#endif
-
-    void swap(preserve_comments& other) {comments.swap(other.comments);}
-
-    void push_back(const std::string& v) {comments.push_back(v);}
-    void push_back(std::string&&      v) {comments.push_back(std::move(v));}
-    void pop_back()                      {comments.pop_back();}
-
-    template<typename ... Ts>
-    void emplace_back(Ts&& ... args) {comments.emplace_back(std::forward<Ts>(args)...);}
-
-    void clear() {comments.clear();}
-
-    size_type size()     const noexcept {return comments.size();}
-    size_type max_size() const noexcept {return comments.max_size();}
-    size_type capacity() const noexcept {return comments.capacity();}
-    bool      empty()    const noexcept {return comments.empty();}
-
-    void reserve(size_type n)                      {comments.reserve(n);}
-    void resize(size_type n)                       {comments.resize(n);}
-    void resize(size_type n, const std::string& c) {comments.resize(n, c);}
-    void shrink_to_fit()                           {comments.shrink_to_fit();}
-
-    reference       operator[](const size_type n)       noexcept {return comments[n];}
-    const_reference operator[](const size_type n) const noexcept {return comments[n];}
-    reference       at(const size_type n)       {return comments.at(n);}
-    const_reference at(const size_type n) const {return comments.at(n);}
-    reference       front()       noexcept {return comments.front();}
-    const_reference front() const noexcept {return comments.front();}
-    reference       back()        noexcept {return comments.back();}
-    const_reference back()  const noexcept {return comments.back();}
-
-    pointer         data()        noexcept {return comments.data();}
-    const_pointer   data()  const noexcept {return comments.data();}
-
-    iterator       begin()        noexcept {return comments.begin();}
-    iterator       end()          noexcept {return comments.end();}
-    const_iterator begin()  const noexcept {return comments.begin();}
-    const_iterator end()    const noexcept {return comments.end();}
-    const_iterator cbegin() const noexcept {return comments.cbegin();}
-    const_iterator cend()   const noexcept {return comments.cend();}
-
-    reverse_iterator       rbegin()        noexcept {return comments.rbegin();}
-    reverse_iterator       rend()          noexcept {return comments.rend();}
-    const_reverse_iterator rbegin()  const noexcept {return comments.rbegin();}
-    const_reverse_iterator rend()    const noexcept {return comments.rend();}
-    const_reverse_iterator crbegin() const noexcept {return comments.crbegin();}
-    const_reverse_iterator crend()   const noexcept {return comments.crend();}
-
-    friend bool operator==(const preserve_comments&, const preserve_comments&);
-    friend bool operator!=(const preserve_comments&, const preserve_comments&);
-    friend bool operator< (const preserve_comments&, const preserve_comments&);
-    friend bool operator<=(const preserve_comments&, const preserve_comments&);
-    friend bool operator> (const preserve_comments&, const preserve_comments&);
-    friend bool operator>=(const preserve_comments&, const preserve_comments&);
-
-    friend void swap(preserve_comments&, std::vector<std::string>&);
-    friend void swap(std::vector<std::string>&, preserve_comments&);
-
-  private:
-
-    container_type comments;
-};
-
-inline bool operator==(const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments == rhs.comments;}
-inline bool operator!=(const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments != rhs.comments;}
-inline bool operator< (const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments <  rhs.comments;}
-inline bool operator<=(const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments <= rhs.comments;}
-inline bool operator> (const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments >  rhs.comments;}
-inline bool operator>=(const preserve_comments& lhs, const preserve_comments& rhs) {return lhs.comments >= rhs.comments;}
-
-inline void swap(preserve_comments& lhs, preserve_comments& rhs)
-{
-    lhs.swap(rhs);
-    return;
-}
-inline void swap(preserve_comments& lhs, std::vector<std::string>& rhs)
-{
-    lhs.comments.swap(rhs);
-    return;
-}
-inline void swap(std::vector<std::string>& lhs, preserve_comments& rhs)
-{
-    lhs.swap(rhs.comments);
-    return;
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const preserve_comments& com)
-{
-    for(const auto& c : com)
-    {
-        os << '#' << c << '\n';
-    }
-    return os;
-}
-
-namespace detail
-{
-
-// To provide the same interface with `preserve_comments`, `discard_comments`
-// should have an iterator. But it does not contain anything, so we need to
-// add an iterator that points nothing.
-//
-// It always points null, so DO NOT unwrap this iterator. It always crashes
-// your program.
-template<typename T, bool is_const>
-struct empty_iterator
-{
-    using value_type        = T;
-    using reference_type    = typename std::conditional<is_const, T const&, T&>::type;
-    using pointer_type      = typename std::conditional<is_const, T const*, T*>::type;
-    using difference_type   = std::ptrdiff_t;
-    using iterator_category = std::random_access_iterator_tag;
-
-    empty_iterator()  = default;
-    ~empty_iterator() = default;
-    empty_iterator(empty_iterator const&) = default;
-    empty_iterator(empty_iterator &&)     = default;
-    empty_iterator& operator=(empty_iterator const&) = default;
-    empty_iterator& operator=(empty_iterator &&)     = default;
-
-    // DO NOT call these operators.
-    reference_type operator*()  const noexcept {std::terminate();}
-    pointer_type   operator->() const noexcept {return nullptr;}
-    reference_type operator[](difference_type) const noexcept {return this->operator*();}
-
-    // These operators do nothing.
-    empty_iterator& operator++()    noexcept {return *this;}
-    empty_iterator  operator++(int) noexcept {return *this;}
-    empty_iterator& operator--()    noexcept {return *this;}
-    empty_iterator  operator--(int) noexcept {return *this;}
-
-    empty_iterator& operator+=(difference_type) noexcept {return *this;}
-    empty_iterator& operator-=(difference_type) noexcept {return *this;}
-
-    empty_iterator  operator+(difference_type) const noexcept {return *this;}
-    empty_iterator  operator-(difference_type) const noexcept {return *this;}
-};
-
-template<typename T, bool C>
-bool operator==(const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return true;}
-template<typename T, bool C>
-bool operator!=(const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return false;}
-template<typename T, bool C>
-bool operator< (const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return false;}
-template<typename T, bool C>
-bool operator<=(const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return true;}
-template<typename T, bool C>
-bool operator> (const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return false;}
-template<typename T, bool C>
-bool operator>=(const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return true;}
-
-template<typename T, bool C>
-typename empty_iterator<T, C>::difference_type
-operator-(const empty_iterator<T, C>&, const empty_iterator<T, C>&) noexcept {return 0;}
-
-template<typename T, bool C>
-empty_iterator<T, C>
-operator+(typename empty_iterator<T, C>::difference_type, const empty_iterator<T, C>& rhs) noexcept {return rhs;}
-template<typename T, bool C>
-empty_iterator<T, C>
-operator+(const empty_iterator<T, C>& lhs, typename empty_iterator<T, C>::difference_type) noexcept {return lhs;}
-
-} // detail
-
-// The default comment type. It discards all the comments. It requires only one
-// byte to contain, so the memory footprint is smaller than preserve_comments.
-//
-// It just ignores `push_back`, `insert`, `erase`, and any other modifications.
-// IT always returns size() == 0, the iterator taken by `begin()` is always the
-// same as that of `end()`, and accessing through `operator[]` or iterators
-// always causes a segmentation fault. DO NOT access to the element of this.
-//
-// Why this is chose as the default type is because the last version (2.x.y)
-// does not contain any comments in a value. To minimize the impact on the
-// efficiency, this is chosen as a default.
-//
-// To reduce the memory footprint, later we can try empty base optimization (EBO).
-struct discard_comments
-{
-    using size_type              = std::size_t;
-    using difference_type        = std::ptrdiff_t;
-    using value_type             = std::string;
-    using reference              = std::string&;
-    using const_reference        = std::string const&;
-    using pointer                = std::string*;
-    using const_pointer          = std::string const*;
-    using iterator               = detail::empty_iterator<std::string, false>;
-    using const_iterator         = detail::empty_iterator<std::string, true>;
-    using reverse_iterator       = detail::empty_iterator<std::string, false>;
-    using const_reverse_iterator = detail::empty_iterator<std::string, true>;
-
-    discard_comments() = default;
-    ~discard_comments() = default;
-    discard_comments(discard_comments const&) = default;
-    discard_comments(discard_comments &&)     = default;
-    discard_comments& operator=(discard_comments const&) = default;
-    discard_comments& operator=(discard_comments &&)     = default;
-
-    explicit discard_comments(const std::vector<std::string>&) noexcept {}
-    explicit discard_comments(std::vector<std::string>&&)      noexcept {}
-    discard_comments& operator=(const std::vector<std::string>&) noexcept {return *this;}
-    discard_comments& operator=(std::vector<std::string>&&)      noexcept {return *this;}
-
-    explicit discard_comments(const preserve_comments&)        noexcept {}
-
-    explicit discard_comments(size_type) noexcept {}
-    discard_comments(size_type, const std::string&) noexcept {}
-    discard_comments(std::initializer_list<std::string>) noexcept {}
-    template<typename InputIterator>
-    discard_comments(InputIterator, InputIterator) noexcept {}
-
-    template<typename InputIterator>
-    void assign(InputIterator, InputIterator)       noexcept {}
-    void assign(std::initializer_list<std::string>) noexcept {}
-    void assign(size_type, const std::string&)      noexcept {}
-
-    iterator insert(const_iterator, const std::string&)                 {return iterator{};}
-    iterator insert(const_iterator, std::string&&)                      {return iterator{};}
-    iterator insert(const_iterator, size_type, const std::string&)      {return iterator{};}
-    template<typename InputIterator>
-    iterator insert(const_iterator, InputIterator, InputIterator)       {return iterator{};}
-    iterator insert(const_iterator, std::initializer_list<std::string>) {return iterator{};}
-
-    template<typename ... Ts>
-    iterator emplace(const_iterator, Ts&& ...)     {return iterator{};}
-    iterator erase(const_iterator)                 {return iterator{};}
-    iterator erase(const_iterator, const_iterator) {return iterator{};}
-
-    void swap(discard_comments&) {return;}
-
-    void push_back(const std::string&) {return;}
-    void push_back(std::string&&     ) {return;}
-    void pop_back()                    {return;}
-
-    template<typename ... Ts>
-    void emplace_back(Ts&& ...) {return;}
-
-    void clear() {return;}
-
-    size_type size()     const noexcept {return 0;}
-    size_type max_size() const noexcept {return 0;}
-    size_type capacity() const noexcept {return 0;}
-    bool      empty()    const noexcept {return true;}
-
-    void reserve(size_type)                    {return;}
-    void resize(size_type)                     {return;}
-    void resize(size_type, const std::string&) {return;}
-    void shrink_to_fit()                       {return;}
-
-    // DO NOT access to the element of this container. This container is always
-    // empty, so accessing through operator[], front/back, data causes address
-    // error.
-
-    reference       operator[](const size_type)       noexcept {return *data();}
-    const_reference operator[](const size_type) const noexcept {return *data();}
-    reference       at(const size_type)       {throw std::out_of_range("toml::discard_comment is always empty.");}
-    const_reference at(const size_type) const {throw std::out_of_range("toml::discard_comment is always empty.");}
-    reference       front()       noexcept {return *data();}
-    const_reference front() const noexcept {return *data();}
-    reference       back()        noexcept {return *data();}
-    const_reference back()  const noexcept {return *data();}
-
-    pointer         data()        noexcept {return nullptr;}
-    const_pointer   data()  const noexcept {return nullptr;}
-
-    iterator       begin()        noexcept {return iterator{};}
-    iterator       end()          noexcept {return iterator{};}
-    const_iterator begin()  const noexcept {return const_iterator{};}
-    const_iterator end()    const noexcept {return const_iterator{};}
-    const_iterator cbegin() const noexcept {return const_iterator{};}
-    const_iterator cend()   const noexcept {return const_iterator{};}
-
-    reverse_iterator       rbegin()        noexcept {return iterator{};}
-    reverse_iterator       rend()          noexcept {return iterator{};}
-    const_reverse_iterator rbegin()  const noexcept {return const_iterator{};}
-    const_reverse_iterator rend()    const noexcept {return const_iterator{};}
-    const_reverse_iterator crbegin() const noexcept {return const_iterator{};}
-    const_reverse_iterator crend()   const noexcept {return const_iterator{};}
-};
-
-inline bool operator==(const discard_comments&, const discard_comments&) noexcept {return true;}
-inline bool operator!=(const discard_comments&, const discard_comments&) noexcept {return false;}
-inline bool operator< (const discard_comments&, const discard_comments&) noexcept {return false;}
-inline bool operator<=(const discard_comments&, const discard_comments&) noexcept {return true;}
-inline bool operator> (const discard_comments&, const discard_comments&) noexcept {return false;}
-inline bool operator>=(const discard_comments&, const discard_comments&) noexcept {return true;}
-
-inline void swap(const discard_comments&, const discard_comments&) noexcept {return;}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const discard_comments&)
-{
-    return os;
-}
-
-} // toml11
-#endif// TOML11_COMMENTS_HPP
diff --git a/src/toml11/toml/datetime.hpp b/src/toml11/toml/datetime.hpp
deleted file mode 100644
index d8127c150..000000000
--- a/src/toml11/toml/datetime.hpp
+++ /dev/null
@@ -1,631 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_DATETIME_HPP
-#define TOML11_DATETIME_HPP
-#include <cstdint>
-#include <cstdlib>
-#include <ctime>
-
-#include <array>
-#include <chrono>
-#include <iomanip>
-#include <ostream>
-#include <tuple>
-
-namespace toml
-{
-
-// To avoid non-threadsafe std::localtime. In C11 (not C++11!), localtime_s is
-// provided in the absolutely same purpose, but C++11 is actually not compatible
-// with C11. We need to dispatch the function depending on the OS.
-namespace detail
-{
-// TODO: find more sophisticated way to handle this
-#if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 1) || defined(_XOPEN_SOURCE) || defined(_BSD_SOURCE) || defined(_SVID_SOURCE) || defined(_POSIX_SOURCE)
-inline std::tm localtime_s(const std::time_t* src)
-{
-    std::tm dst;
-    const auto result = ::localtime_r(src, &dst);
-    if (!result) { throw std::runtime_error("localtime_r failed."); }
-    return dst;
-}
-inline std::tm gmtime_s(const std::time_t* src)
-{
-    std::tm dst;
-    const auto result = ::gmtime_r(src, &dst);
-    if (!result) { throw std::runtime_error("gmtime_r failed."); }
-    return dst;
-}
-#elif defined(_MSC_VER)
-inline std::tm localtime_s(const std::time_t* src)
-{
-    std::tm dst;
-    const auto result = ::localtime_s(&dst, src);
-    if (result) { throw std::runtime_error("localtime_s failed."); }
-    return dst;
-}
-inline std::tm gmtime_s(const std::time_t* src)
-{
-    std::tm dst;
-    const auto result = ::gmtime_s(&dst, src);
-    if (result) { throw std::runtime_error("gmtime_s failed."); }
-    return dst;
-}
-#else // fallback. not threadsafe
-inline std::tm localtime_s(const std::time_t* src)
-{
-    const auto result = std::localtime(src);
-    if (!result) { throw std::runtime_error("localtime failed."); }
-    return *result;
-}
-inline std::tm gmtime_s(const std::time_t* src)
-{
-    const auto result = std::gmtime(src);
-    if (!result) { throw std::runtime_error("gmtime failed."); }
-    return *result;
-}
-#endif
-} // detail
-
-enum class month_t : std::uint8_t
-{
-    Jan =  0,
-    Feb =  1,
-    Mar =  2,
-    Apr =  3,
-    May =  4,
-    Jun =  5,
-    Jul =  6,
-    Aug =  7,
-    Sep =  8,
-    Oct =  9,
-    Nov = 10,
-    Dec = 11
-};
-
-struct local_date
-{
-    std::int16_t year;   // A.D. (like, 2018)
-    std::uint8_t month;  // [0, 11]
-    std::uint8_t day;    // [1, 31]
-
-    local_date(int y, month_t m, int d)
-        : year (static_cast<std::int16_t>(y)),
-          month(static_cast<std::uint8_t>(m)),
-          day  (static_cast<std::uint8_t>(d))
-    {}
-
-    explicit local_date(const std::tm& t)
-        : year (static_cast<std::int16_t>(t.tm_year + 1900)),
-          month(static_cast<std::uint8_t>(t.tm_mon)),
-          day  (static_cast<std::uint8_t>(t.tm_mday))
-    {}
-
-    explicit local_date(const std::chrono::system_clock::time_point& tp)
-    {
-        const auto t    = std::chrono::system_clock::to_time_t(tp);
-        const auto time = detail::localtime_s(&t);
-        *this = local_date(time);
-    }
-
-    explicit local_date(const std::time_t t)
-        : local_date(std::chrono::system_clock::from_time_t(t))
-    {}
-
-    operator std::chrono::system_clock::time_point() const
-    {
-        // std::mktime returns date as local time zone. no conversion needed
-        std::tm t;
-        t.tm_sec   = 0;
-        t.tm_min   = 0;
-        t.tm_hour  = 0;
-        t.tm_mday  = static_cast<int>(this->day);
-        t.tm_mon   = static_cast<int>(this->month);
-        t.tm_year  = static_cast<int>(this->year) - 1900;
-        t.tm_wday  = 0; // the value will be ignored
-        t.tm_yday  = 0; // the value will be ignored
-        t.tm_isdst = -1;
-        return std::chrono::system_clock::from_time_t(std::mktime(&t));
-    }
-
-    operator std::time_t() const
-    {
-        return std::chrono::system_clock::to_time_t(
-                std::chrono::system_clock::time_point(*this));
-    }
-
-    local_date() = default;
-    ~local_date() = default;
-    local_date(local_date const&) = default;
-    local_date(local_date&&)      = default;
-    local_date& operator=(local_date const&) = default;
-    local_date& operator=(local_date&&)      = default;
-};
-
-inline bool operator==(const local_date& lhs, const local_date& rhs)
-{
-    return std::make_tuple(lhs.year, lhs.month, lhs.day) ==
-           std::make_tuple(rhs.year, rhs.month, rhs.day);
-}
-inline bool operator!=(const local_date& lhs, const local_date& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator< (const local_date& lhs, const local_date& rhs)
-{
-    return std::make_tuple(lhs.year, lhs.month, lhs.day) <
-           std::make_tuple(rhs.year, rhs.month, rhs.day);
-}
-inline bool operator<=(const local_date& lhs, const local_date& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-inline bool operator> (const local_date& lhs, const local_date& rhs)
-{
-    return !(lhs <= rhs);
-}
-inline bool operator>=(const local_date& lhs, const local_date& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const local_date& date)
-{
-    os << std::setfill('0') << std::setw(4) << static_cast<int>(date.year )     << '-';
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(date.month) + 1 << '-';
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(date.day  )    ;
-    return os;
-}
-
-struct local_time
-{
-    std::uint8_t  hour;        // [0, 23]
-    std::uint8_t  minute;      // [0, 59]
-    std::uint8_t  second;      // [0, 60]
-    std::uint16_t millisecond; // [0, 999]
-    std::uint16_t microsecond; // [0, 999]
-    std::uint16_t nanosecond;  // [0, 999]
-
-    local_time(int h, int m, int s,
-               int ms = 0, int us = 0, int ns = 0)
-        : hour  (static_cast<std::uint8_t>(h)),
-          minute(static_cast<std::uint8_t>(m)),
-          second(static_cast<std::uint8_t>(s)),
-          millisecond(static_cast<std::uint16_t>(ms)),
-          microsecond(static_cast<std::uint16_t>(us)),
-          nanosecond (static_cast<std::uint16_t>(ns))
-    {}
-
-    explicit local_time(const std::tm& t)
-        : hour  (static_cast<std::uint8_t>(t.tm_hour)),
-          minute(static_cast<std::uint8_t>(t.tm_min)),
-          second(static_cast<std::uint8_t>(t.tm_sec)),
-          millisecond(0), microsecond(0), nanosecond(0)
-    {}
-
-    template<typename Rep, typename Period>
-    explicit local_time(const std::chrono::duration<Rep, Period>& t)
-    {
-        const auto h = std::chrono::duration_cast<std::chrono::hours>(t);
-        this->hour = static_cast<std::uint8_t>(h.count());
-        const auto t2 = t - h;
-        const auto m = std::chrono::duration_cast<std::chrono::minutes>(t2);
-        this->minute = static_cast<std::uint8_t>(m.count());
-        const auto t3 = t2 - m;
-        const auto s = std::chrono::duration_cast<std::chrono::seconds>(t3);
-        this->second = static_cast<std::uint8_t>(s.count());
-        const auto t4 = t3 - s;
-        const auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(t4);
-        this->millisecond = static_cast<std::uint16_t>(ms.count());
-        const auto t5 = t4 - ms;
-        const auto us = std::chrono::duration_cast<std::chrono::microseconds>(t5);
-        this->microsecond = static_cast<std::uint16_t>(us.count());
-        const auto t6 = t5 - us;
-        const auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(t6);
-        this->nanosecond = static_cast<std::uint16_t>(ns.count());
-    }
-
-    operator std::chrono::nanoseconds() const
-    {
-        return std::chrono::nanoseconds (this->nanosecond)  +
-               std::chrono::microseconds(this->microsecond) +
-               std::chrono::milliseconds(this->millisecond) +
-               std::chrono::seconds(this->second) +
-               std::chrono::minutes(this->minute) +
-               std::chrono::hours(this->hour);
-    }
-
-    local_time() = default;
-    ~local_time() = default;
-    local_time(local_time const&) = default;
-    local_time(local_time&&)      = default;
-    local_time& operator=(local_time const&) = default;
-    local_time& operator=(local_time&&)      = default;
-};
-
-inline bool operator==(const local_time& lhs, const local_time& rhs)
-{
-    return std::make_tuple(lhs.hour, lhs.minute, lhs.second, lhs.millisecond, lhs.microsecond, lhs.nanosecond) ==
-           std::make_tuple(rhs.hour, rhs.minute, rhs.second, rhs.millisecond, rhs.microsecond, rhs.nanosecond);
-}
-inline bool operator!=(const local_time& lhs, const local_time& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator< (const local_time& lhs, const local_time& rhs)
-{
-    return std::make_tuple(lhs.hour, lhs.minute, lhs.second, lhs.millisecond, lhs.microsecond, lhs.nanosecond) <
-           std::make_tuple(rhs.hour, rhs.minute, rhs.second, rhs.millisecond, rhs.microsecond, rhs.nanosecond);
-}
-inline bool operator<=(const local_time& lhs, const local_time& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-inline bool operator> (const local_time& lhs, const local_time& rhs)
-{
-    return !(lhs <= rhs);
-}
-inline bool operator>=(const local_time& lhs, const local_time& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const local_time& time)
-{
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(time.hour  ) << ':';
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(time.minute) << ':';
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(time.second);
-    if(time.millisecond != 0 || time.microsecond != 0 || time.nanosecond != 0)
-    {
-        os << '.';
-        os << std::setfill('0') << std::setw(3) << static_cast<int>(time.millisecond);
-        if(time.microsecond != 0 || time.nanosecond != 0)
-        {
-            os << std::setfill('0') << std::setw(3) << static_cast<int>(time.microsecond);
-            if(time.nanosecond != 0)
-            {
-                os << std::setfill('0') << std::setw(3) << static_cast<int>(time.nanosecond);
-            }
-        }
-    }
-    return os;
-}
-
-struct time_offset
-{
-    std::int8_t hour;   // [-12, 12]
-    std::int8_t minute; // [-59, 59]
-
-    time_offset(int h, int m)
-        : hour  (static_cast<std::int8_t>(h)),
-          minute(static_cast<std::int8_t>(m))
-    {}
-
-    operator std::chrono::minutes() const
-    {
-        return std::chrono::minutes(this->minute) +
-               std::chrono::hours(this->hour);
-    }
-
-    time_offset() = default;
-    ~time_offset() = default;
-    time_offset(time_offset const&) = default;
-    time_offset(time_offset&&)      = default;
-    time_offset& operator=(time_offset const&) = default;
-    time_offset& operator=(time_offset&&)      = default;
-};
-
-inline bool operator==(const time_offset& lhs, const time_offset& rhs)
-{
-    return std::make_tuple(lhs.hour, lhs.minute) ==
-           std::make_tuple(rhs.hour, rhs.minute);
-}
-inline bool operator!=(const time_offset& lhs, const time_offset& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator< (const time_offset& lhs, const time_offset& rhs)
-{
-    return std::make_tuple(lhs.hour, lhs.minute) <
-           std::make_tuple(rhs.hour, rhs.minute);
-}
-inline bool operator<=(const time_offset& lhs, const time_offset& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-inline bool operator> (const time_offset& lhs, const time_offset& rhs)
-{
-    return !(lhs <= rhs);
-}
-inline bool operator>=(const time_offset& lhs, const time_offset& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const time_offset& offset)
-{
-    if(offset.hour == 0 && offset.minute == 0)
-    {
-        os << 'Z';
-        return os;
-    }
-    int minute = static_cast<int>(offset.hour) * 60 + offset.minute;
-    if(minute < 0){os << '-'; minute = std::abs(minute);} else {os << '+';}
-    os << std::setfill('0') << std::setw(2) << minute / 60 << ':';
-    os << std::setfill('0') << std::setw(2) << minute % 60;
-    return os;
-}
-
-struct local_datetime
-{
-    local_date date;
-    local_time time;
-
-    local_datetime(local_date d, local_time t): date(d), time(t) {}
-
-    explicit local_datetime(const std::tm& t): date(t), time(t){}
-
-    explicit local_datetime(const std::chrono::system_clock::time_point& tp)
-    {
-        const auto t = std::chrono::system_clock::to_time_t(tp);
-        std::tm ltime = detail::localtime_s(&t);
-
-        this->date = local_date(ltime);
-        this->time = local_time(ltime);
-
-        // std::tm lacks subsecond information, so diff between tp and tm
-        // can be used to get millisecond & microsecond information.
-        const auto t_diff = tp -
-            std::chrono::system_clock::from_time_t(std::mktime(&ltime));
-        this->time.millisecond = static_cast<std::uint16_t>(
-          std::chrono::duration_cast<std::chrono::milliseconds>(t_diff).count());
-        this->time.microsecond = static_cast<std::uint16_t>(
-          std::chrono::duration_cast<std::chrono::microseconds>(t_diff).count());
-        this->time.nanosecond = static_cast<std::uint16_t>(
-          std::chrono::duration_cast<std::chrono::nanoseconds >(t_diff).count());
-    }
-
-    explicit local_datetime(const std::time_t t)
-        : local_datetime(std::chrono::system_clock::from_time_t(t))
-    {}
-
-    operator std::chrono::system_clock::time_point() const
-    {
-        using internal_duration =
-            typename std::chrono::system_clock::time_point::duration;
-
-        // Normally DST begins at A.M. 3 or 4. If we re-use conversion operator
-        // of local_date and local_time independently, the conversion fails if
-        // it is the day when DST begins or ends. Since local_date considers the
-        // time is 00:00 A.M. and local_time does not consider DST because it
-        // does not have any date information. We need to consider both date and
-        // time information at the same time to convert it correctly.
-
-        std::tm t;
-        t.tm_sec   = static_cast<int>(this->time.second);
-        t.tm_min   = static_cast<int>(this->time.minute);
-        t.tm_hour  = static_cast<int>(this->time.hour);
-        t.tm_mday  = static_cast<int>(this->date.day);
-        t.tm_mon   = static_cast<int>(this->date.month);
-        t.tm_year  = static_cast<int>(this->date.year) - 1900;
-        t.tm_wday  = 0; // the value will be ignored
-        t.tm_yday  = 0; // the value will be ignored
-        t.tm_isdst = -1;
-
-        // std::mktime returns date as local time zone. no conversion needed
-        auto dt = std::chrono::system_clock::from_time_t(std::mktime(&t));
-        dt += std::chrono::duration_cast<internal_duration>(
-                std::chrono::milliseconds(this->time.millisecond) +
-                std::chrono::microseconds(this->time.microsecond) +
-                std::chrono::nanoseconds (this->time.nanosecond));
-        return dt;
-    }
-
-    operator std::time_t() const
-    {
-        return std::chrono::system_clock::to_time_t(
-                std::chrono::system_clock::time_point(*this));
-    }
-
-    local_datetime() = default;
-    ~local_datetime() = default;
-    local_datetime(local_datetime const&) = default;
-    local_datetime(local_datetime&&)      = default;
-    local_datetime& operator=(local_datetime const&) = default;
-    local_datetime& operator=(local_datetime&&)      = default;
-};
-
-inline bool operator==(const local_datetime& lhs, const local_datetime& rhs)
-{
-    return std::make_tuple(lhs.date, lhs.time) ==
-           std::make_tuple(rhs.date, rhs.time);
-}
-inline bool operator!=(const local_datetime& lhs, const local_datetime& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator< (const local_datetime& lhs, const local_datetime& rhs)
-{
-    return std::make_tuple(lhs.date, lhs.time) <
-           std::make_tuple(rhs.date, rhs.time);
-}
-inline bool operator<=(const local_datetime& lhs, const local_datetime& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-inline bool operator> (const local_datetime& lhs, const local_datetime& rhs)
-{
-    return !(lhs <= rhs);
-}
-inline bool operator>=(const local_datetime& lhs, const local_datetime& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const local_datetime& dt)
-{
-    os << dt.date << 'T' << dt.time;
-    return os;
-}
-
-struct offset_datetime
-{
-    local_date  date;
-    local_time  time;
-    time_offset offset;
-
-    offset_datetime(local_date d, local_time t, time_offset o)
-        : date(d), time(t), offset(o)
-    {}
-    offset_datetime(const local_datetime& dt, time_offset o)
-        : date(dt.date), time(dt.time), offset(o)
-    {}
-    explicit offset_datetime(const local_datetime& ld)
-        : date(ld.date), time(ld.time), offset(get_local_offset(nullptr))
-          // use the current local timezone offset
-    {}
-    explicit offset_datetime(const std::chrono::system_clock::time_point& tp)
-        : offset(0, 0) // use gmtime
-    {
-        const auto timet = std::chrono::system_clock::to_time_t(tp);
-        const auto tm    = detail::gmtime_s(&timet);
-        this->date = local_date(tm);
-        this->time = local_time(tm);
-    }
-    explicit offset_datetime(const std::time_t& t)
-        : offset(0, 0) // use gmtime
-    {
-        const auto tm    = detail::gmtime_s(&t);
-        this->date = local_date(tm);
-        this->time = local_time(tm);
-    }
-    explicit offset_datetime(const std::tm& t)
-        : offset(0, 0) // assume gmtime
-    {
-        this->date = local_date(t);
-        this->time = local_time(t);
-    }
-
-    operator std::chrono::system_clock::time_point() const
-    {
-        // get date-time
-        using internal_duration =
-            typename std::chrono::system_clock::time_point::duration;
-
-        // first, convert it to local date-time information in the same way as
-        // local_datetime does. later we will use time_t to adjust time offset.
-        std::tm t;
-        t.tm_sec   = static_cast<int>(this->time.second);
-        t.tm_min   = static_cast<int>(this->time.minute);
-        t.tm_hour  = static_cast<int>(this->time.hour);
-        t.tm_mday  = static_cast<int>(this->date.day);
-        t.tm_mon   = static_cast<int>(this->date.month);
-        t.tm_year  = static_cast<int>(this->date.year) - 1900;
-        t.tm_wday  = 0; // the value will be ignored
-        t.tm_yday  = 0; // the value will be ignored
-        t.tm_isdst = -1;
-        const std::time_t tp_loc = std::mktime(std::addressof(t));
-
-        auto tp = std::chrono::system_clock::from_time_t(tp_loc);
-        tp += std::chrono::duration_cast<internal_duration>(
-                std::chrono::milliseconds(this->time.millisecond) +
-                std::chrono::microseconds(this->time.microsecond) +
-                std::chrono::nanoseconds (this->time.nanosecond));
-
-        // Since mktime uses local time zone, it should be corrected.
-        // `12:00:00+09:00` means `03:00:00Z`. So mktime returns `03:00:00Z` if
-        // we are in `+09:00` timezone. To represent `12:00:00Z` there, we need
-        // to add `+09:00` to `03:00:00Z`.
-        //    Here, it uses the time_t converted from date-time info to handle
-        // daylight saving time.
-        const auto ofs = get_local_offset(std::addressof(tp_loc));
-        tp += std::chrono::hours  (ofs.hour);
-        tp += std::chrono::minutes(ofs.minute);
-
-        // We got `12:00:00Z` by correcting local timezone applied by mktime.
-        // Then we will apply the offset. Let's say `12:00:00-08:00` is given.
-        // And now, we have `12:00:00Z`. `12:00:00-08:00` means `20:00:00Z`.
-        // So we need to subtract the offset.
-        tp -= std::chrono::minutes(this->offset);
-        return tp;
-    }
-
-    operator std::time_t() const
-    {
-        return std::chrono::system_clock::to_time_t(
-                std::chrono::system_clock::time_point(*this));
-    }
-
-    offset_datetime() = default;
-    ~offset_datetime() = default;
-    offset_datetime(offset_datetime const&) = default;
-    offset_datetime(offset_datetime&&)      = default;
-    offset_datetime& operator=(offset_datetime const&) = default;
-    offset_datetime& operator=(offset_datetime&&)      = default;
-
-  private:
-
-    static time_offset get_local_offset(const std::time_t* tp)
-    {
-        // get local timezone with the same date-time information as mktime
-        const auto t = detail::localtime_s(tp);
-
-        std::array<char, 6> buf;
-        const auto result = std::strftime(buf.data(), 6, "%z", &t); // +hhmm\0
-        if(result != 5)
-        {
-            throw std::runtime_error("toml::offset_datetime: cannot obtain "
-                                     "timezone information of current env");
-        }
-        const int ofs = std::atoi(buf.data());
-        const int ofs_h = ofs / 100;
-        const int ofs_m = ofs - (ofs_h * 100);
-        return time_offset(ofs_h, ofs_m);
-    }
-};
-
-inline bool operator==(const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return std::make_tuple(lhs.date, lhs.time, lhs.offset) ==
-           std::make_tuple(rhs.date, rhs.time, rhs.offset);
-}
-inline bool operator!=(const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator< (const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return std::make_tuple(lhs.date, lhs.time, lhs.offset) <
-           std::make_tuple(rhs.date, rhs.time, rhs.offset);
-}
-inline bool operator<=(const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-inline bool operator> (const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return !(lhs <= rhs);
-}
-inline bool operator>=(const offset_datetime& lhs, const offset_datetime& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const offset_datetime& dt)
-{
-    os << dt.date << 'T' << dt.time << dt.offset;
-    return os;
-}
-
-}//toml
-#endif// TOML11_DATETIME
diff --git a/src/toml11/toml/exception.hpp b/src/toml11/toml/exception.hpp
deleted file mode 100644
index c64651d0a..000000000
--- a/src/toml11/toml/exception.hpp
+++ /dev/null
@@ -1,65 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_EXCEPTION_HPP
-#define TOML11_EXCEPTION_HPP
-#include <stdexcept>
-#include <string>
-
-#include "source_location.hpp"
-
-namespace toml
-{
-
-struct exception : public std::exception
-{
-  public:
-    explicit exception(const source_location& loc): loc_(loc) {}
-    virtual ~exception() noexcept override = default;
-    virtual const char* what() const noexcept override {return "";}
-    virtual source_location const& location() const noexcept {return loc_;}
-
-  protected:
-    source_location loc_;
-};
-
-struct syntax_error : public toml::exception
-{
-  public:
-    explicit syntax_error(const std::string& what_arg, const source_location& loc)
-        : exception(loc), what_(what_arg)
-    {}
-    virtual ~syntax_error() noexcept override = default;
-    virtual const char* what() const noexcept override {return what_.c_str();}
-
-  protected:
-    std::string what_;
-};
-
-struct type_error : public toml::exception
-{
-  public:
-    explicit type_error(const std::string& what_arg, const source_location& loc)
-        : exception(loc), what_(what_arg)
-    {}
-    virtual ~type_error() noexcept override = default;
-    virtual const char* what() const noexcept override {return what_.c_str();}
-
-  protected:
-    std::string what_;
-};
-
-struct internal_error : public toml::exception
-{
-  public:
-    explicit internal_error(const std::string& what_arg, const source_location& loc)
-        : exception(loc), what_(what_arg)
-    {}
-    virtual ~internal_error() noexcept override = default;
-    virtual const char* what() const noexcept override {return what_.c_str();}
-
-  protected:
-    std::string what_;
-};
-
-} // toml
-#endif // TOML_EXCEPTION
diff --git a/src/toml11/toml/from.hpp b/src/toml11/toml/from.hpp
deleted file mode 100644
index 10815caf5..000000000
--- a/src/toml11/toml/from.hpp
+++ /dev/null
@@ -1,19 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_FROM_HPP
-#define TOML11_FROM_HPP
-
-namespace toml
-{
-
-template<typename T>
-struct from;
-// {
-//     static T from_toml(const toml::value& v)
-//     {
-//         // User-defined conversions ...
-//     }
-// };
-
-} // toml
-#endif // TOML11_FROM_HPP
diff --git a/src/toml11/toml/get.hpp b/src/toml11/toml/get.hpp
deleted file mode 100644
index d7fdf553b..000000000
--- a/src/toml11/toml/get.hpp
+++ /dev/null
@@ -1,1117 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_GET_HPP
-#define TOML11_GET_HPP
-#include <algorithm>
-
-#include "from.hpp"
-#include "result.hpp"
-#include "value.hpp"
-
-namespace toml
-{
-
-// ============================================================================
-// exact toml::* type
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T> &
-get(basic_value<C, M, V>& v)
-{
-    return v.template cast<detail::type_to_enum<T, basic_value<C, M, V>>::value>();
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T> const&
-get(const basic_value<C, M, V>& v)
-{
-    return v.template cast<detail::type_to_enum<T, basic_value<C, M, V>>::value>();
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T>
-get(basic_value<C, M, V>&& v)
-{
-    return T(std::move(v).template cast<detail::type_to_enum<T, basic_value<C, M, V>>::value>());
-}
-
-// ============================================================================
-// T == toml::value; identity transformation.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, basic_value<C, M, V>>::value, T>&
-get(basic_value<C, M, V>& v)
-{
-    return v;
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, basic_value<C, M, V>>::value, T> const&
-get(const basic_value<C, M, V>& v)
-{
-    return v;
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, basic_value<C, M, V>>::value, T>
-get(basic_value<C, M, V>&& v)
-{
-    return basic_value<C, M, V>(std::move(v));
-}
-
-// ============================================================================
-// T == toml::basic_value<C2, M2, V2>; basic_value -> basic_value
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<detail::conjunction<detail::is_basic_value<T>,
-    detail::negation<std::is_same<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return T(v);
-}
-
-// ============================================================================
-// integer convertible from toml::Integer
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<detail::conjunction<
-    std::is_integral<T>,                            // T is integral
-    detail::negation<std::is_same<T, bool>>,        // but not bool
-    detail::negation<                               // but not toml::integer
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return static_cast<T>(v.as_integer());
-}
-
-// ============================================================================
-// floating point convertible from toml::Float
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<detail::conjunction<
-    std::is_floating_point<T>,                      // T is floating_point
-    detail::negation<                               // but not toml::floating
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return static_cast<T>(v.as_floating());
-}
-
-// ============================================================================
-// std::string; toml uses its own toml::string, but it should be convertible to
-// std::string seamlessly
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, std::string>::value, std::string>&
-get(basic_value<C, M, V>& v)
-{
-    return v.as_string().str;
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, std::string>::value, std::string> const&
-get(const basic_value<C, M, V>& v)
-{
-    return v.as_string().str;
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, std::string>::value, std::string>
-get(basic_value<C, M, V>&& v)
-{
-    return std::string(std::move(v.as_string().str));
-}
-
-// ============================================================================
-// std::string_view
-
-#if defined(TOML11_USING_STRING_VIEW) && TOML11_USING_STRING_VIEW>0
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<std::is_same<T, std::string_view>::value, std::string_view>
-get(const basic_value<C, M, V>& v)
-{
-    return std::string_view(v.as_string().str);
-}
-#endif
-
-// ============================================================================
-// std::chrono::duration from toml::local_time.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<detail::is_chrono_duration<T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return std::chrono::duration_cast<T>(
-            std::chrono::nanoseconds(v.as_local_time()));
-}
-
-// ============================================================================
-// std::chrono::system_clock::time_point from toml::datetime variants
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-inline detail::enable_if_t<
-    std::is_same<std::chrono::system_clock::time_point, T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    switch(v.type())
-    {
-        case value_t::local_date:
-        {
-            return std::chrono::system_clock::time_point(v.as_local_date());
-        }
-        case value_t::local_datetime:
-        {
-            return std::chrono::system_clock::time_point(v.as_local_datetime());
-        }
-        case value_t::offset_datetime:
-        {
-            return std::chrono::system_clock::time_point(v.as_offset_datetime());
-        }
-        default:
-        {
-            throw type_error(detail::format_underline("toml::value: "
-                "bad_cast to std::chrono::system_clock::time_point", {
-                    {v.location(), concat_to_string("the actual type is ", v.type())}
-                }), v.location());
-        }
-    }
-}
-
-// ============================================================================
-// forward declaration to use this recursively. ignore this and go ahead.
-
-// array-like type with push_back(value) method
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_container<T>,         // T is a container
-    detail::has_push_back_method<T>, // T::push_back(value) works
-    detail::negation<                // but not toml::array
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>&);
-
-// array-like type without push_back(value) method
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_container<T>,                           // T is a container
-    detail::negation<detail::has_push_back_method<T>>, // w/o push_back(...)
-    detail::negation<                                  // not toml::array
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>&);
-
-// std::pair<T1, T2>
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_std_pair<T>::value, T>
-get(const basic_value<C, M, V>&);
-
-// std::tuple<T1, T2, ...>
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_std_tuple<T>::value, T>
-get(const basic_value<C, M, V>&);
-
-// map-like classes
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_map<T>, // T is map
-    detail::negation<  // but not toml::table
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>&);
-
-// T.from_toml(v)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::negation<                         // not a toml::* type
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>,
-    detail::has_from_toml_method<T, C, M, V>, // but has from_toml(toml::value)
-    std::is_default_constructible<T>          // and default constructible
-    >::value, T>
-get(const basic_value<C, M, V>&);
-
-// toml::from<T>::from_toml(v)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::has_specialized_from<T>::value, T>
-get(const basic_value<C, M, V>&);
-
-// T(const toml::value&) and T is not toml::basic_value,
-// and it does not have `from<T>` nor `from_toml`.
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::negation<detail::is_basic_value<T>>,
-    std::is_constructible<T, const basic_value<C, M, V>&>,
-    detail::negation<detail::has_from_toml_method<T, C, M, V>>,
-    detail::negation<detail::has_specialized_from<T>>
-    >::value, T>
-get(const basic_value<C, M, V>&);
-
-// ============================================================================
-// array-like types; most likely STL container, like std::vector, etc.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_container<T>,         // T is a container
-    detail::has_push_back_method<T>, // container.push_back(elem) works
-    detail::negation<                // but not toml::array
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    using value_type = typename T::value_type;
-    const auto& ary = v.as_array();
-
-    T container;
-    try_reserve(container, ary.size());
-
-    for(const auto& elem : ary)
-    {
-        container.push_back(get<value_type>(elem));
-    }
-    return container;
-}
-
-// ============================================================================
-// std::forward_list does not have push_back, insert, or emplace.
-// It has insert_after, emplace_after, push_front.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_std_forward_list<T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    using value_type = typename T::value_type;
-    T container;
-    for(const auto& elem : v.as_array())
-    {
-        container.push_front(get<value_type>(elem));
-    }
-    container.reverse();
-    return container;
-}
-
-// ============================================================================
-// array-like types, without push_back(). most likely [std|boost]::array.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_container<T>,                           // T is a container
-    detail::negation<detail::has_push_back_method<T>>, // w/o push_back
-    detail::negation<                                  // T is not toml::array
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    using value_type = typename T::value_type;
-    const auto& ar = v.as_array();
-
-    T container;
-    if(ar.size() != container.size())
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "toml::get: specified container size is ", container.size(),
-            " but there are ", ar.size(), " elements in toml array."), {
-                {v.location(), "here"}
-            }));
-    }
-    for(std::size_t i=0; i<ar.size(); ++i)
-    {
-        container[i] = ::toml::get<value_type>(ar[i]);
-    }
-    return container;
-}
-
-// ============================================================================
-// std::pair.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_std_pair<T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    using first_type  = typename T::first_type;
-    using second_type = typename T::second_type;
-
-    const auto& ar = v.as_array();
-    if(ar.size() != 2)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "toml::get: specified std::pair but there are ", ar.size(),
-            " elements in toml array."), {{v.location(), "here"}}));
-    }
-    return std::make_pair(::toml::get<first_type >(ar.at(0)),
-                          ::toml::get<second_type>(ar.at(1)));
-}
-
-// ============================================================================
-// std::tuple.
-
-namespace detail
-{
-template<typename T, typename Array, std::size_t ... I>
-T get_tuple_impl(const Array& a, index_sequence<I...>)
-{
-    return std::make_tuple(
-        ::toml::get<typename std::tuple_element<I, T>::type>(a.at(I))...);
-}
-} // detail
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_std_tuple<T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    const auto& ar = v.as_array();
-    if(ar.size() != std::tuple_size<T>::value)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "toml::get: specified std::tuple with ",
-            std::tuple_size<T>::value, " elements, but there are ", ar.size(),
-            " elements in toml array."), {{v.location(), "here"}}));
-    }
-    return detail::get_tuple_impl<T>(ar,
-            detail::make_index_sequence<std::tuple_size<T>::value>{});
-}
-
-// ============================================================================
-// map-like types; most likely STL map, like std::map or std::unordered_map.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::is_map<T>, // T is map
-    detail::negation<  // but not toml::array
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    using key_type    = typename T::key_type;
-    using mapped_type = typename T::mapped_type;
-    static_assert(std::is_convertible<std::string, key_type>::value,
-                  "toml::get only supports map type of which key_type is "
-                  "convertible from std::string.");
-    T map;
-    for(const auto& kv : v.as_table())
-    {
-        map.emplace(key_type(kv.first), get<mapped_type>(kv.second));
-    }
-    return map;
-}
-
-// ============================================================================
-// user-defined, but compatible types.
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::negation<                         // not a toml::* type
-        detail::is_exact_toml_type<T, basic_value<C, M, V>>>,
-    detail::has_from_toml_method<T, C, M, V>, // but has from_toml(toml::value) memfn
-    std::is_default_constructible<T>          // and default constructible
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    T ud;
-    ud.from_toml(v);
-    return ud;
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::has_specialized_from<T>::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return ::toml::from<T>::from_toml(v);
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::negation<detail::is_basic_value<T>>,                // T is not a toml::value
-    std::is_constructible<T, const basic_value<C, M, V>&>,      // T is constructible from toml::value
-    detail::negation<detail::has_from_toml_method<T, C, M, V>>, // and T does not have T.from_toml(v);
-    detail::negation<detail::has_specialized_from<T>>           // and T does not have toml::from<T>{};
-    >::value, T>
-get(const basic_value<C, M, V>& v)
-{
-    return T(v);
-}
-
-// ============================================================================
-// find
-
-// ----------------------------------------------------------------------------
-// these overloads do not require to set T. and returns value itself.
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> const& find(const basic_value<C, M, V>& v, const key& ky)
-{
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return tab.at(ky);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>& find(basic_value<C, M, V>& v, const key& ky)
-{
-    auto& tab = v.as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return tab.at(ky);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> find(basic_value<C, M, V>&& v, const key& ky)
-{
-    typename basic_value<C, M, V>::table_type tab = std::move(v).as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return basic_value<C, M, V>(std::move(tab.at(ky)));
-}
-
-// ----------------------------------------------------------------------------
-// find(value, idx)
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> const&
-find(const basic_value<C, M, V>& v, const std::size_t idx)
-{
-    const auto& ary = v.as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return ary.at(idx);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>& find(basic_value<C, M, V>& v, const std::size_t idx)
-{
-    auto& ary = v.as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return ary.at(idx);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> find(basic_value<C, M, V>&& v, const std::size_t idx)
-{
-    auto& ary = v.as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return basic_value<C, M, V>(std::move(ary.at(idx)));
-}
-
-// ----------------------------------------------------------------------------
-// find<T>(value, key);
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V> const&>()))
-find(const basic_value<C, M, V>& v, const key& ky)
-{
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return ::toml::get<T>(tab.at(ky));
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&>()))
-find(basic_value<C, M, V>& v, const key& ky)
-{
-    auto& tab = v.as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return ::toml::get<T>(tab.at(ky));
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&&>()))
-find(basic_value<C, M, V>&& v, const key& ky)
-{
-    typename basic_value<C, M, V>::table_type tab = std::move(v).as_table();
-    if(tab.count(ky) == 0)
-    {
-        detail::throw_key_not_found_error(v, ky);
-    }
-    return ::toml::get<T>(std::move(tab.at(ky)));
-}
-
-// ----------------------------------------------------------------------------
-// find<T>(value, idx)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V> const&>()))
-find(const basic_value<C, M, V>& v, const std::size_t idx)
-{
-    const auto& ary = v.as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return ::toml::get<T>(ary.at(idx));
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&>()))
-find(basic_value<C, M, V>& v, const std::size_t idx)
-{
-    auto& ary = v.as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return ::toml::get<T>(ary.at(idx));
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&&>()))
-find(basic_value<C, M, V>&& v, const std::size_t idx)
-{
-    typename basic_value<C, M, V>::array_type ary = std::move(v).as_array();
-    if(ary.size() <= idx)
-    {
-        throw std::out_of_range(detail::format_underline(concat_to_string(
-            "index ", idx, " is out of range"), {{v.location(), "in this array"}}));
-    }
-    return ::toml::get<T>(std::move(ary.at(idx)));
-}
-
-// --------------------------------------------------------------------------
-// toml::find(toml::value, toml::key, Ts&& ... keys)
-
-namespace detail
-{
-// It suppresses warnings by -Wsign-conversion. Let's say we have the following
-// code.
-// ```cpp
-// const auto x = toml::find<std::string>(data, "array", 0);
-// ```
-// Here, the type of literal number `0` is `int`. `int` is a signed integer.
-// `toml::find` takes `std::size_t` as an index. So it causes implicit sign
-// conversion and `-Wsign-conversion` warns about it. Using `0u` instead of `0`
-// suppresses the warning, but it makes user code messy.
-//     To suppress this warning, we need to be aware of type conversion caused
-// by `toml::find(v, key1, key2, ... keys)`. But the thing is that the types of
-// keys can be any combination of {string-like, size_t-like}. Of course we can't
-// write down all the combinations. Thus we need to use some function that
-// recognize the type of argument and cast it into `std::string` or
-// `std::size_t` depending on the context.
-//     `key_cast` does the job. It has 2 overloads. One is invoked when the
-// argument type is an integer and cast the argument into `std::size_t`. The
-// other is invoked when the argument type is not an integer, possibly one of
-// std::string, const char[N] or const char*, and construct std::string from
-// the argument.
-//     `toml::find(v, k1, k2, ... ks)` uses `key_cast` before passing `ks` to
-// `toml::find(v, k)` to suppress -Wsign-conversion.
-
-template<typename T>
-enable_if_t<conjunction<std::is_integral<remove_cvref_t<T>>,
-            negation<std::is_same<remove_cvref_t<T>, bool>>>::value, std::size_t>
-key_cast(T&& v) noexcept
-{
-    return std::size_t(v);
-}
-template<typename T>
-enable_if_t<negation<conjunction<std::is_integral<remove_cvref_t<T>>,
-            negation<std::is_same<remove_cvref_t<T>, bool>>>>::value, std::string>
-key_cast(T&& v) noexcept
-{
-    return std::string(std::forward<T>(v));
-}
-} // detail
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-const basic_value<C, M, V>&
-find(const basic_value<C, M, V>& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find(::toml::find(v, detail::key_cast(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-basic_value<C, M, V>&
-find(basic_value<C, M, V>& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find(::toml::find(v, detail::key_cast(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-basic_value<C, M, V>
-find(basic_value<C, M, V>&& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find(::toml::find(std::move(v), std::forward<Key1>(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-decltype(::toml::get<T>(std::declval<const basic_value<C, M, V>&>()))
-find(const basic_value<C, M, V>& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find<T>(::toml::find(v, detail::key_cast(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&>()))
-find(basic_value<C, M, V>& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find<T>(::toml::find(v, detail::key_cast(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         typename Key1, typename Key2, typename ... Keys>
-decltype(::toml::get<T>(std::declval<basic_value<C, M, V>&&>()))
-find(basic_value<C, M, V>&& v, Key1&& k1, Key2&& k2, Keys&& ... keys)
-{
-    return ::toml::find<T>(::toml::find(std::move(v), detail::key_cast(k1)),
-            detail::key_cast(k2), std::forward<Keys>(keys)...);
-}
-
-// ============================================================================
-// get_or(value, fallback)
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> const&
-get_or(const basic_value<C, M, V>& v, const basic_value<C, M, V>&)
-{
-    return v;
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>&
-get_or(basic_value<C, M, V>& v, basic_value<C, M, V>&)
-{
-    return v;
-}
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>
-get_or(basic_value<C, M, V>&& v, basic_value<C, M, V>&&)
-{
-    return v;
-}
-
-// ----------------------------------------------------------------------------
-// specialization for the exact toml types (return type becomes lvalue ref)
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T> const&
-get_or(const basic_value<C, M, V>& v, const T& opt)
-{
-    try
-    {
-        return get<detail::remove_cvref_t<T>>(v);
-    }
-    catch(...)
-    {
-        return opt;
-    }
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T>&
-get_or(basic_value<C, M, V>& v, T& opt)
-{
-    try
-    {
-        return get<detail::remove_cvref_t<T>>(v);
-    }
-    catch(...)
-    {
-        return opt;
-    }
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_exact_toml_type<detail::remove_cvref_t<T>,
-    basic_value<C, M, V>>::value, detail::remove_cvref_t<T>>
-get_or(basic_value<C, M, V>&& v, T&& opt)
-{
-    try
-    {
-        return get<detail::remove_cvref_t<T>>(std::move(v));
-    }
-    catch(...)
-    {
-        return detail::remove_cvref_t<T>(std::forward<T>(opt));
-    }
-}
-
-// ----------------------------------------------------------------------------
-// specialization for std::string (return type becomes lvalue ref)
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<std::is_same<detail::remove_cvref_t<T>, std::string>::value,
-    std::string> const&
-get_or(const basic_value<C, M, V>& v, const T& opt)
-{
-    try
-    {
-        return v.as_string().str;
-    }
-    catch(...)
-    {
-        return opt;
-    }
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<std::is_same<T, std::string>::value, std::string>&
-get_or(basic_value<C, M, V>& v, T& opt)
-{
-    try
-    {
-        return v.as_string().str;
-    }
-    catch(...)
-    {
-        return opt;
-    }
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    std::is_same<detail::remove_cvref_t<T>, std::string>::value, std::string>
-get_or(basic_value<C, M, V>&& v, T&& opt)
-{
-    try
-    {
-        return std::move(v.as_string().str);
-    }
-    catch(...)
-    {
-        return std::string(std::forward<T>(opt));
-    }
-}
-
-// ----------------------------------------------------------------------------
-// specialization for string literal
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::is_string_literal<
-    typename std::remove_reference<T>::type>::value, std::string>
-get_or(const basic_value<C, M, V>& v, T&& opt)
-{
-    try
-    {
-        return std::move(v.as_string().str);
-    }
-    catch(...)
-    {
-        return std::string(std::forward<T>(opt));
-    }
-}
-
-// ----------------------------------------------------------------------------
-// others (require type conversion and return type cannot be lvalue reference)
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    detail::negation<detail::is_exact_toml_type<detail::remove_cvref_t<T>,
-        basic_value<C, M, V>>>,
-    detail::negation<std::is_same<std::string, detail::remove_cvref_t<T>>>,
-    detail::negation<detail::is_string_literal<
-        typename std::remove_reference<T>::type>>
-    >::value, detail::remove_cvref_t<T>>
-get_or(const basic_value<C, M, V>& v, T&& opt)
-{
-    try
-    {
-        return get<detail::remove_cvref_t<T>>(v);
-    }
-    catch(...)
-    {
-        return detail::remove_cvref_t<T>(std::forward<T>(opt));
-    }
-}
-
-// ===========================================================================
-// find_or(value, key, fallback)
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V> const&
-find_or(const basic_value<C, M, V>& v, const key& ky,
-        const basic_value<C, M, V>& opt)
-{
-    if(!v.is_table()) {return opt;}
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return tab.at(ky);
-}
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>&
-find_or(basic_value<C, M, V>& v, const toml::key& ky, basic_value<C, M, V>& opt)
-{
-    if(!v.is_table()) {return opt;}
-    auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return tab.at(ky);
-}
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-basic_value<C, M, V>
-find_or(basic_value<C, M, V>&& v, const toml::key& ky, basic_value<C, M, V>&& opt)
-{
-    if(!v.is_table()) {return opt;}
-    auto tab = std::move(v).as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return basic_value<C, M, V>(std::move(tab.at(ky)));
-}
-
-// ---------------------------------------------------------------------------
-// exact types (return type can be a reference)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T> const&
-find_or(const basic_value<C, M, V>& v, const key& ky, const T& opt)
-{
-    if(!v.is_table()) {return opt;}
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return get_or(tab.at(ky), opt);
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_exact_toml_type<T, basic_value<C, M, V>>::value, T>&
-find_or(basic_value<C, M, V>& v, const toml::key& ky, T& opt)
-{
-    if(!v.is_table()) {return opt;}
-    auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return get_or(tab.at(ky), opt);
-}
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_exact_toml_type<T, basic_value<C, M, V>>::value,
-    detail::remove_cvref_t<T>>
-find_or(basic_value<C, M, V>&& v, const toml::key& ky, T&& opt)
-{
-    if(!v.is_table()) {return std::forward<T>(opt);}
-    auto tab = std::move(v).as_table();
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
-    return get_or(std::move(tab.at(ky)), std::forward<T>(opt));
-}
-
-// ---------------------------------------------------------------------------
-// std::string (return type can be a reference)
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<std::is_same<T, std::string>::value, std::string> const&
-find_or(const basic_value<C, M, V>& v, const key& ky, const T& opt)
-{
-    if(!v.is_table()) {return opt;}
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return get_or(tab.at(ky), opt);
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<std::is_same<T, std::string>::value, std::string>&
-find_or(basic_value<C, M, V>& v, const toml::key& ky, T& opt)
-{
-    if(!v.is_table()) {return opt;}
-    auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return opt;}
-    return get_or(tab.at(ky), opt);
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<std::is_same<T, std::string>::value, std::string>
-find_or(basic_value<C, M, V>&& v, const toml::key& ky, T&& opt)
-{
-    if(!v.is_table()) {return std::forward<T>(opt);}
-    auto tab = std::move(v).as_table();
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
-    return get_or(std::move(tab.at(ky)), std::forward<T>(opt));
-}
-
-// ---------------------------------------------------------------------------
-// string literal (deduced as std::string)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<
-    detail::is_string_literal<typename std::remove_reference<T>::type>::value,
-    std::string>
-find_or(const basic_value<C, M, V>& v, const toml::key& ky, T&& opt)
-{
-    if(!v.is_table()) {return std::string(opt);}
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return std::string(opt);}
-    return get_or(tab.at(ky), std::forward<T>(opt));
-}
-
-// ---------------------------------------------------------------------------
-// others (require type conversion and return type cannot be lvalue reference)
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-detail::enable_if_t<detail::conjunction<
-    // T is not an exact toml type
-    detail::negation<detail::is_exact_toml_type<
-        detail::remove_cvref_t<T>, basic_value<C, M, V>>>,
-    // T is not std::string
-    detail::negation<std::is_same<std::string, detail::remove_cvref_t<T>>>,
-    // T is not a string literal
-    detail::negation<detail::is_string_literal<
-        typename std::remove_reference<T>::type>>
-    >::value, detail::remove_cvref_t<T>>
-find_or(const basic_value<C, M, V>& v, const toml::key& ky, T&& opt)
-{
-    if(!v.is_table()) {return std::forward<T>(opt);}
-    const auto& tab = v.as_table();
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
-    return get_or(tab.at(ky), std::forward<T>(opt));
-}
-
-// ---------------------------------------------------------------------------
-// recursive find-or with type deduction (find_or(value, keys, opt))
-
-template<typename Value, typename ... Ks,
-         typename detail::enable_if_t<(sizeof...(Ks) > 1), std::nullptr_t> = nullptr>
-         // here we need to add SFINAE in the template parameter to avoid
-         // infinite recursion in type deduction on gcc
-auto find_or(Value&& v, const toml::key& ky, Ks&& ... keys)
-    -> decltype(find_or(std::forward<Value>(v), ky, detail::last_one(std::forward<Ks>(keys)...)))
-{
-    if(!v.is_table())
-    {
-        return detail::last_one(std::forward<Ks>(keys)...);
-    }
-    auto&& tab = std::forward<Value>(v).as_table();
-    if(tab.count(ky) == 0)
-    {
-        return detail::last_one(std::forward<Ks>(keys)...);
-    }
-    return find_or(std::forward<decltype(tab)>(tab).at(ky), std::forward<Ks>(keys)...);
-}
-
-// ---------------------------------------------------------------------------
-// recursive find_or with explicit type specialization, find_or<int>(value, keys...)
-
-template<typename T, typename Value, typename ... Ks,
-         typename detail::enable_if_t<(sizeof...(Ks) > 1), std::nullptr_t> = nullptr>
-         // here we need to add SFINAE in the template parameter to avoid
-         // infinite recursion in type deduction on gcc
-auto find_or(Value&& v, const toml::key& ky, Ks&& ... keys)
-    -> decltype(find_or<T>(std::forward<Value>(v), ky, detail::last_one(std::forward<Ks>(keys)...)))
-{
-    if(!v.is_table())
-    {
-        return detail::last_one(std::forward<Ks>(keys)...);
-    }
-    auto&& tab = std::forward<Value>(v).as_table();
-    if(tab.count(ky) == 0)
-    {
-        return detail::last_one(std::forward<Ks>(keys)...);
-    }
-    return find_or(std::forward<decltype(tab)>(tab).at(ky), std::forward<Ks>(keys)...);
-}
-
-// ============================================================================
-// expect
-
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-result<T, std::string> expect(const basic_value<C, M, V>& v) noexcept
-{
-    try
-    {
-        return ok(get<T>(v));
-    }
-    catch(const std::exception& e)
-    {
-        return err(e.what());
-    }
-}
-template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-result<T, std::string>
-expect(const basic_value<C, M, V>& v, const toml::key& k) noexcept
-{
-    try
-    {
-        return ok(find<T>(v, k));
-    }
-    catch(const std::exception& e)
-    {
-        return err(e.what());
-    }
-}
-
-} // toml
-#endif// TOML11_GET
diff --git a/src/toml11/toml/into.hpp b/src/toml11/toml/into.hpp
deleted file mode 100644
index 74495560e..000000000
--- a/src/toml11/toml/into.hpp
+++ /dev/null
@@ -1,19 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_INTO_HPP
-#define TOML11_INTO_HPP
-
-namespace toml
-{
-
-template<typename T>
-struct into;
-// {
-//     static toml::value into_toml(const T& user_defined_type)
-//     {
-//         // User-defined conversions ...
-//     }
-// };
-
-} // toml
-#endif // TOML11_INTO_HPP
diff --git a/src/toml11/toml/lexer.hpp b/src/toml11/toml/lexer.hpp
deleted file mode 100644
index ea5050b8d..000000000
--- a/src/toml11/toml/lexer.hpp
+++ /dev/null
@@ -1,293 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_LEXER_HPP
-#define TOML11_LEXER_HPP
-#include <istream>
-#include <sstream>
-#include <stdexcept>
-#include <fstream>
-
-#include "combinator.hpp"
-
-namespace toml
-{
-namespace detail
-{
-
-// these scans contents from current location in a container of char
-// and extract a region that matches their own pattern.
-// to see the implementation of each component, see combinator.hpp.
-
-using lex_wschar  = either<character<' '>, character<'\t'>>;
-using lex_ws      = repeat<lex_wschar, at_least<1>>;
-using lex_newline = either<character<'\n'>,
-                           sequence<character<'\r'>, character<'\n'>>>;
-using lex_lower   = in_range<'a', 'z'>;
-using lex_upper   = in_range<'A', 'Z'>;
-using lex_alpha   = either<lex_lower, lex_upper>;
-using lex_digit   = in_range<'0', '9'>;
-using lex_nonzero = in_range<'1', '9'>;
-using lex_oct_dig = in_range<'0', '7'>;
-using lex_bin_dig = in_range<'0', '1'>;
-using lex_hex_dig = either<lex_digit, in_range<'A', 'F'>, in_range<'a', 'f'>>;
-
-using lex_hex_prefix = sequence<character<'0'>, character<'x'>>;
-using lex_oct_prefix = sequence<character<'0'>, character<'o'>>;
-using lex_bin_prefix = sequence<character<'0'>, character<'b'>>;
-using lex_underscore = character<'_'>;
-using lex_plus       = character<'+'>;
-using lex_minus      = character<'-'>;
-using lex_sign       = either<lex_plus, lex_minus>;
-
-// digit | nonzero 1*(digit | _ digit)
-using lex_unsigned_dec_int = either<sequence<lex_nonzero, repeat<
-    either<lex_digit, sequence<lex_underscore, lex_digit>>, at_least<1>>>,
-    lex_digit>;
-// (+|-)? unsigned_dec_int
-using lex_dec_int = sequence<maybe<lex_sign>, lex_unsigned_dec_int>;
-
-// hex_prefix hex_dig *(hex_dig | _ hex_dig)
-using lex_hex_int = sequence<lex_hex_prefix, sequence<lex_hex_dig, repeat<
-    either<lex_hex_dig, sequence<lex_underscore, lex_hex_dig>>, unlimited>>>;
-// oct_prefix oct_dig *(oct_dig | _ oct_dig)
-using lex_oct_int = sequence<lex_oct_prefix, sequence<lex_oct_dig, repeat<
-    either<lex_oct_dig, sequence<lex_underscore, lex_oct_dig>>, unlimited>>>;
-// bin_prefix bin_dig *(bin_dig | _ bin_dig)
-using lex_bin_int = sequence<lex_bin_prefix, sequence<lex_bin_dig, repeat<
-    either<lex_bin_dig, sequence<lex_underscore, lex_bin_dig>>, unlimited>>>;
-
-// (dec_int | hex_int | oct_int | bin_int)
-using lex_integer = either<lex_bin_int, lex_oct_int, lex_hex_int, lex_dec_int>;
-
-// ===========================================================================
-
-using lex_inf = sequence<character<'i'>, character<'n'>, character<'f'>>;
-using lex_nan = sequence<character<'n'>, character<'a'>, character<'n'>>;
-using lex_special_float = sequence<maybe<lex_sign>, either<lex_inf, lex_nan>>;
-
-using lex_zero_prefixable_int = sequence<lex_digit, repeat<either<lex_digit,
-    sequence<lex_underscore, lex_digit>>, unlimited>>;
-
-using lex_fractional_part = sequence<character<'.'>, lex_zero_prefixable_int>;
-
-using lex_exponent_part   = sequence<either<character<'e'>, character<'E'>>,
-        maybe<lex_sign>, lex_zero_prefixable_int>;
-
-using lex_float = either<lex_special_float,
-      sequence<lex_dec_int, either<lex_exponent_part,
-      sequence<lex_fractional_part, maybe<lex_exponent_part>>>>>;
-
-// ===========================================================================
-
-using lex_true = sequence<character<'t'>, character<'r'>,
-                          character<'u'>, character<'e'>>;
-using lex_false = sequence<character<'f'>, character<'a'>, character<'l'>,
-                           character<'s'>, character<'e'>>;
-using lex_boolean = either<lex_true, lex_false>;
-
-// ===========================================================================
-
-using lex_date_fullyear = repeat<lex_digit, exactly<4>>;
-using lex_date_month    = repeat<lex_digit, exactly<2>>;
-using lex_date_mday     = repeat<lex_digit, exactly<2>>;
-using lex_time_delim    = either<character<'T'>, character<'t'>, character<' '>>;
-using lex_time_hour     = repeat<lex_digit, exactly<2>>;
-using lex_time_minute   = repeat<lex_digit, exactly<2>>;
-using lex_time_second   = repeat<lex_digit, exactly<2>>;
-using lex_time_secfrac  = sequence<character<'.'>,
-                                   repeat<lex_digit, at_least<1>>>;
-
-using lex_time_numoffset = sequence<either<character<'+'>, character<'-'>>,
-                                    sequence<lex_time_hour, character<':'>,
-                                             lex_time_minute>>;
-using lex_time_offset = either<character<'Z'>, character<'z'>,
-                               lex_time_numoffset>;
-
-using lex_partial_time = sequence<lex_time_hour,   character<':'>,
-                                  lex_time_minute, character<':'>,
-                                  lex_time_second, maybe<lex_time_secfrac>>;
-using lex_full_date    = sequence<lex_date_fullyear, character<'-'>,
-                                  lex_date_month,    character<'-'>,
-                                  lex_date_mday>;
-using lex_full_time    = sequence<lex_partial_time, lex_time_offset>;
-
-using lex_offset_date_time = sequence<lex_full_date, lex_time_delim, lex_full_time>;
-using lex_local_date_time  = sequence<lex_full_date, lex_time_delim, lex_partial_time>;
-using lex_local_date       = lex_full_date;
-using lex_local_time       = lex_partial_time;
-
-// ===========================================================================
-
-using lex_quotation_mark  = character<'"'>;
-using lex_basic_unescaped = exclude<either<in_range<0x00, 0x08>, // 0x09 (tab) is allowed
-                                           in_range<0x0A, 0x1F>,
-                                           character<0x22>, character<0x5C>,
-                                           character<0x7F>>>;
-
-using lex_escape          = character<'\\'>;
-using lex_escape_unicode_short = sequence<character<'u'>,
-                                          repeat<lex_hex_dig, exactly<4>>>;
-using lex_escape_unicode_long  = sequence<character<'U'>,
-                                          repeat<lex_hex_dig, exactly<8>>>;
-using lex_escape_seq_char = either<character<'"'>, character<'\\'>,
-                                   character<'b'>, character<'f'>,
-                                   character<'n'>, character<'r'>,
-                                   character<'t'>,
-                                   lex_escape_unicode_short,
-                                   lex_escape_unicode_long
-                                   >;
-using lex_escaped      = sequence<lex_escape, lex_escape_seq_char>;
-using lex_basic_char   = either<lex_basic_unescaped, lex_escaped>;
-using lex_basic_string = sequence<lex_quotation_mark,
-                                  repeat<lex_basic_char, unlimited>,
-                                  lex_quotation_mark>;
-
-// After toml post-v0.5.0, it is explicitly clarified how quotes in ml-strings
-// are allowed to be used.
-// After this, the following strings are *explicitly* allowed.
-// - One or two `"`s in a multi-line basic string is allowed wherever it is.
-// - Three consecutive `"`s in a multi-line basic string is considered as a delimiter.
-// - One or two `"`s can appear just before or after the delimiter.
-// ```toml
-// str4 = """Here are two quotation marks: "". Simple enough."""
-// str5 = """Here are three quotation marks: ""\"."""
-// str6 = """Here are fifteen quotation marks: ""\"""\"""\"""\"""\"."""
-// str7 = """"This," she said, "is just a pointless statement.""""
-// ```
-// In the current implementation (v3.3.0), it is difficult to parse `str7` in
-// the above example. It is difficult to recognize `"` at the end of string body
-// collectly. It will be misunderstood as a `"""` delimiter and an additional,
-// invalid `"`. Like this:
-// ```console
-//   what():  [error] toml::parse_table: invalid line format
-//  --> hoge.toml
-//     |
-//  13 | str7 = """"This," she said, "is just a pointless statement.""""
-//     |                                                               ^- expected newline, but got '"'.
-// ```
-// As a quick workaround for this problem, `lex_ml_basic_string_delim` was
-// split into two, `lex_ml_basic_string_open` and `lex_ml_basic_string_close`.
-// `lex_ml_basic_string_open` allows only `"""`. `_close` allows 3-5 `"`s.
-// In parse_ml_basic_string() function, the trailing `"`s will be attached to
-// the string body.
-//
-using lex_ml_basic_string_delim = repeat<lex_quotation_mark, exactly<3>>;
-using lex_ml_basic_string_open  = lex_ml_basic_string_delim;
-using lex_ml_basic_string_close = sequence<
-        repeat<lex_quotation_mark, exactly<3>>,
-        maybe<lex_quotation_mark>, maybe<lex_quotation_mark>
-    >;
-
-using lex_ml_basic_unescaped    = exclude<either<in_range<0x00, 0x08>, // 0x09 is tab
-                                                 in_range<0x0A, 0x1F>,
-                                                 character<0x5C>, // backslash
-                                                 character<0x7F>, // DEL
-                                                 lex_ml_basic_string_delim>>;
-
-using lex_ml_basic_escaped_newline = sequence<
-        lex_escape, maybe<lex_ws>, lex_newline,
-        repeat<either<lex_ws, lex_newline>, unlimited>>;
-
-using lex_ml_basic_char = either<lex_ml_basic_unescaped, lex_escaped>;
-using lex_ml_basic_body = repeat<either<lex_ml_basic_char, lex_newline,
-                                        lex_ml_basic_escaped_newline>,
-                                 unlimited>;
-using lex_ml_basic_string = sequence<lex_ml_basic_string_open,
-                                     lex_ml_basic_body,
-                                     lex_ml_basic_string_close>;
-
-using lex_literal_char = exclude<either<in_range<0x00, 0x08>, in_range<0x0A, 0x1F>,
-                                        character<0x7F>, character<0x27>>>;
-using lex_apostrophe = character<'\''>;
-using lex_literal_string = sequence<lex_apostrophe,
-                                    repeat<lex_literal_char, unlimited>,
-                                    lex_apostrophe>;
-
-// the same reason as above.
-using lex_ml_literal_string_delim = repeat<lex_apostrophe, exactly<3>>;
-using lex_ml_literal_string_open  = lex_ml_literal_string_delim;
-using lex_ml_literal_string_close = sequence<
-        repeat<lex_apostrophe, exactly<3>>,
-        maybe<lex_apostrophe>, maybe<lex_apostrophe>
-    >;
-
-using lex_ml_literal_char = exclude<either<in_range<0x00, 0x08>,
-                                           in_range<0x0A, 0x1F>,
-                                           character<0x7F>,
-                                           lex_ml_literal_string_delim>>;
-using lex_ml_literal_body = repeat<either<lex_ml_literal_char, lex_newline>,
-                                   unlimited>;
-using lex_ml_literal_string = sequence<lex_ml_literal_string_open,
-                                       lex_ml_literal_body,
-                                       lex_ml_literal_string_close>;
-
-using lex_string = either<lex_ml_basic_string,   lex_basic_string,
-                          lex_ml_literal_string, lex_literal_string>;
-
-// ===========================================================================
-using lex_dot_sep = sequence<maybe<lex_ws>, character<'.'>, maybe<lex_ws>>;
-
-using lex_unquoted_key = repeat<either<lex_alpha, lex_digit,
-                                       character<'-'>, character<'_'>>,
-                                at_least<1>>;
-using lex_quoted_key = either<lex_basic_string, lex_literal_string>;
-using lex_simple_key = either<lex_unquoted_key, lex_quoted_key>;
-using lex_dotted_key = sequence<lex_simple_key,
-                                repeat<sequence<lex_dot_sep, lex_simple_key>,
-                                       at_least<1>
-                                       >
-                                >;
-using lex_key = either<lex_dotted_key, lex_simple_key>;
-
-using lex_keyval_sep = sequence<maybe<lex_ws>,
-                                character<'='>,
-                                maybe<lex_ws>>;
-
-using lex_std_table_open  = character<'['>;
-using lex_std_table_close = character<']'>;
-using lex_std_table       = sequence<lex_std_table_open,
-                                     maybe<lex_ws>,
-                                     lex_key,
-                                     maybe<lex_ws>,
-                                     lex_std_table_close>;
-
-using lex_array_table_open  = sequence<lex_std_table_open,  lex_std_table_open>;
-using lex_array_table_close = sequence<lex_std_table_close, lex_std_table_close>;
-using lex_array_table       = sequence<lex_array_table_open,
-                                       maybe<lex_ws>,
-                                       lex_key,
-                                       maybe<lex_ws>,
-                                       lex_array_table_close>;
-
-using lex_utf8_1byte = in_range<0x00, 0x7F>;
-using lex_utf8_2byte = sequence<
-        in_range<static_cast<char>(0xC2), static_cast<char>(0xDF)>,
-        in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>
-    >;
-using lex_utf8_3byte = sequence<either<
-        sequence<character<static_cast<char>(0xE0)>,                          in_range<static_cast<char>(0xA0), static_cast<char>(0xBF)>>,
-        sequence<in_range <static_cast<char>(0xE1), static_cast<char>(0xEC)>, in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>>,
-        sequence<character<static_cast<char>(0xED)>,                          in_range<static_cast<char>(0x80), static_cast<char>(0x9F)>>,
-        sequence<in_range <static_cast<char>(0xEE), static_cast<char>(0xEF)>, in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>>
-    >, in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>>;
-using lex_utf8_4byte = sequence<either<
-        sequence<character<static_cast<char>(0xF0)>,                          in_range<static_cast<char>(0x90), static_cast<char>(0xBF)>>,
-        sequence<in_range <static_cast<char>(0xF1), static_cast<char>(0xF3)>, in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>>,
-        sequence<character<static_cast<char>(0xF4)>,                          in_range<static_cast<char>(0x80), static_cast<char>(0x8F)>>
-    >, in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>,
-       in_range<static_cast<char>(0x80), static_cast<char>(0xBF)>>;
-using lex_utf8_code = either<
-        lex_utf8_1byte,
-        lex_utf8_2byte,
-        lex_utf8_3byte,
-        lex_utf8_4byte
-    >;
-
-using lex_comment_start_symbol = character<'#'>;
-using lex_non_eol_ascii = either<character<0x09>, in_range<0x20, 0x7E>>;
-using lex_comment = sequence<lex_comment_start_symbol, repeat<either<
-    lex_non_eol_ascii, lex_utf8_2byte, lex_utf8_3byte, lex_utf8_4byte>, unlimited>>;
-
-} // detail
-} // toml
-#endif // TOML_LEXER_HPP
diff --git a/src/toml11/toml/literal.hpp b/src/toml11/toml/literal.hpp
deleted file mode 100644
index 04fbbc13e..000000000
--- a/src/toml11/toml/literal.hpp
+++ /dev/null
@@ -1,113 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_LITERAL_HPP
-#define TOML11_LITERAL_HPP
-#include "parser.hpp"
-
-namespace toml
-{
-inline namespace literals
-{
-inline namespace toml_literals
-{
-
-// implementation
-inline ::toml::basic_value<TOML11_DEFAULT_COMMENT_STRATEGY, std::unordered_map, std::vector>
-literal_internal_impl(::toml::detail::location loc)
-{
-    using value_type = ::toml::basic_value<
-        TOML11_DEFAULT_COMMENT_STRATEGY, std::unordered_map, std::vector>;
-    // if there are some comments or empty lines, skip them.
-    using skip_line = ::toml::detail::repeat<toml::detail::sequence<
-            ::toml::detail::maybe<::toml::detail::lex_ws>,
-            ::toml::detail::maybe<::toml::detail::lex_comment>,
-            ::toml::detail::lex_newline
-        >, ::toml::detail::at_least<1>>;
-    skip_line::invoke(loc);
-
-    // if there are some whitespaces before a value, skip them.
-    using skip_ws = ::toml::detail::repeat<
-        ::toml::detail::lex_ws, ::toml::detail::at_least<1>>;
-    skip_ws::invoke(loc);
-
-    // to distinguish arrays and tables, first check it is a table or not.
-    //
-    // "[1,2,3]"_toml;   // this is an array
-    // "[table]"_toml;   // a table that has an empty table named "table" inside.
-    // "[[1,2,3]]"_toml; // this is an array of arrays
-    // "[[table]]"_toml; // this is a table that has an array of tables inside.
-    //
-    // "[[1]]"_toml;     // this can be both... (currently it becomes a table)
-    // "1 = [{}]"_toml;  // this is a table that has an array of table named 1.
-    // "[[1,]]"_toml;    // this is an array of arrays.
-    // "[[1],]"_toml;    // this also.
-
-    const auto the_front = loc.iter();
-
-    const bool is_table_key = ::toml::detail::lex_std_table::invoke(loc);
-    loc.reset(the_front);
-
-    const bool is_aots_key  = ::toml::detail::lex_array_table::invoke(loc);
-    loc.reset(the_front);
-
-    // If it is neither a table-key or a array-of-table-key, it may be a value.
-    if(!is_table_key && !is_aots_key)
-    {
-        if(auto data = ::toml::detail::parse_value<value_type>(loc))
-        {
-            return data.unwrap();
-        }
-    }
-
-    // Note that still it can be a table, because the literal might be something
-    // like the following.
-    // ```cpp
-    // R"( // c++11 raw string literals
-    //   key = "value"
-    //   int = 42
-    // )"_toml;
-    // ```
-    // It is a valid toml file.
-    // It should be parsed as if we parse a file with this content.
-
-    if(auto data = ::toml::detail::parse_toml_file<value_type>(loc))
-    {
-        return data.unwrap();
-    }
-    else // none of them.
-    {
-        throw ::toml::syntax_error(data.unwrap_err(), source_location(loc));
-    }
-
-}
-
-inline ::toml::basic_value<TOML11_DEFAULT_COMMENT_STRATEGY, std::unordered_map, std::vector>
-operator"" _toml(const char* str, std::size_t len)
-{
-    ::toml::detail::location loc(
-            std::string("TOML literal encoded in a C++ code"),
-            std::vector<char>(str, str + len));
-    // literal length does not include the null character at the end.
-    return literal_internal_impl(std::move(loc));
-}
-
-// value of __cplusplus in C++2a/20 mode is not fixed yet along compilers.
-// So here we use the feature test macro for `char8_t` itself.
-#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
-// value of u8"" literal has been changed from char to char8_t and char8_t is
-// NOT compatible to char
-inline ::toml::basic_value<TOML11_DEFAULT_COMMENT_STRATEGY, std::unordered_map, std::vector>
-operator"" _toml(const char8_t* str, std::size_t len)
-{
-    ::toml::detail::location loc(
-            std::string("TOML literal encoded in a C++ code"),
-            std::vector<char>(reinterpret_cast<const char*>(str),
-                              reinterpret_cast<const char*>(str) + len));
-    return literal_internal_impl(std::move(loc));
-}
-#endif
-
-} // toml_literals
-} // literals
-} // toml
-#endif//TOML11_LITERAL_HPP
diff --git a/src/toml11/toml/macros.hpp b/src/toml11/toml/macros.hpp
deleted file mode 100644
index e8f91aecd..000000000
--- a/src/toml11/toml/macros.hpp
+++ /dev/null
@@ -1,121 +0,0 @@
-#ifndef TOML11_MACROS_HPP
-#define TOML11_MACROS_HPP
-
-#define TOML11_STRINGIZE_AUX(x) #x
-#define TOML11_STRINGIZE(x)     TOML11_STRINGIZE_AUX(x)
-
-#define TOML11_CONCATENATE_AUX(x, y) x##y
-#define TOML11_CONCATENATE(x, y)     TOML11_CONCATENATE_AUX(x, y)
-
-// ============================================================================
-// TOML11_DEFINE_CONVERSION_NON_INTRUSIVE
-
-#ifndef TOML11_WITHOUT_DEFINE_NON_INTRUSIVE
-
-// ----------------------------------------------------------------------------
-// TOML11_ARGS_SIZE
-
-#define TOML11_INDEX_RSEQ() \
-    32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, \
-    16, 15, 14, 13, 12, 11, 10,  9,  8,  7,  6,  5,  4,  3,  2,  1, 0
-#define TOML11_ARGS_SIZE_IMPL(\
-    ARG1,  ARG2,  ARG3,  ARG4,  ARG5,  ARG6,  ARG7,  ARG8,  ARG9,  ARG10, \
-    ARG11, ARG12, ARG13, ARG14, ARG15, ARG16, ARG17, ARG18, ARG19, ARG20, \
-    ARG21, ARG22, ARG23, ARG24, ARG25, ARG26, ARG27, ARG28, ARG29, ARG30, \
-    ARG31, ARG32, N, ...) N
-#define TOML11_ARGS_SIZE_AUX(...) TOML11_ARGS_SIZE_IMPL(__VA_ARGS__)
-#define TOML11_ARGS_SIZE(...) TOML11_ARGS_SIZE_AUX(__VA_ARGS__, TOML11_INDEX_RSEQ())
-
-// ----------------------------------------------------------------------------
-// TOML11_FOR_EACH_VA_ARGS
-
-#define TOML11_FOR_EACH_VA_ARGS_AUX_1( FUNCTOR, ARG1     ) FUNCTOR(ARG1)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_2( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_1( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_3( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_2( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_4( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_3( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_5( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_4( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_6( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_5( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_7( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_6( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_8( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_7( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_9( FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_8( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_10(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_9( FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_11(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_10(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_12(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_11(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_13(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_12(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_14(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_13(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_15(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_14(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_16(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_15(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_17(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_16(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_18(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_17(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_19(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_18(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_20(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_19(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_21(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_20(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_22(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_21(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_23(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_22(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_24(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_23(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_25(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_24(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_26(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_25(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_27(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_26(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_28(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_27(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_29(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_28(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_30(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_29(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_31(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_30(FUNCTOR, __VA_ARGS__)
-#define TOML11_FOR_EACH_VA_ARGS_AUX_32(FUNCTOR, ARG1, ...) FUNCTOR(ARG1) TOML11_FOR_EACH_VA_ARGS_AUX_31(FUNCTOR, __VA_ARGS__)
-
-#define TOML11_FOR_EACH_VA_ARGS(FUNCTOR, ...)\
-    TOML11_CONCATENATE(TOML11_FOR_EACH_VA_ARGS_AUX_, TOML11_ARGS_SIZE(__VA_ARGS__))(FUNCTOR, __VA_ARGS__)
-
-// ----------------------------------------------------------------------------
-// TOML11_DEFINE_CONVERSION_NON_INTRUSIVE
-
-// use it in the following way.
-// ```cpp
-// namespace foo
-// {
-// struct Foo
-// {
-//     std::string s;
-//     double      d;
-//     int         i;
-// };
-// } // foo
-//
-// TOML11_DEFINE_CONVERSION_NON_INTRUSIVE(foo::Foo, s, d, i)
-// ```
-// And then you can use `toml::find<foo::Foo>(file, "foo");`
-//
-#define TOML11_FIND_MEMBER_VARIABLE_FROM_VALUE(VAR_NAME)\
-    obj.VAR_NAME = toml::find<decltype(obj.VAR_NAME)>(v, TOML11_STRINGIZE(VAR_NAME));
-
-#define TOML11_ASSIGN_MEMBER_VARIABLE_TO_VALUE(VAR_NAME)\
-    v[TOML11_STRINGIZE(VAR_NAME)] = obj.VAR_NAME;
-
-#define TOML11_DEFINE_CONVERSION_NON_INTRUSIVE(NAME, ...)\
-    namespace toml {                                                                     \
-    template<>                                                                           \
-    struct from<NAME>                                                                    \
-    {                                                                                    \
-        template<typename C, template<typename ...> class T,                             \
-                 template<typename ...> class A>                                         \
-        static NAME from_toml(const basic_value<C, T, A>& v)                             \
-        {                                                                                \
-            NAME obj;                                                                    \
-            TOML11_FOR_EACH_VA_ARGS(TOML11_FIND_MEMBER_VARIABLE_FROM_VALUE, __VA_ARGS__) \
-            return obj;                                                                  \
-        }                                                                                \
-    };                                                                                   \
-    template<>                                                                           \
-    struct into<NAME>                                                                    \
-    {                                                                                    \
-        static value into_toml(const NAME& obj)                                          \
-        {                                                                                \
-            ::toml::value v = ::toml::table{};                                           \
-            TOML11_FOR_EACH_VA_ARGS(TOML11_ASSIGN_MEMBER_VARIABLE_TO_VALUE, __VA_ARGS__) \
-            return v;                                                                    \
-        }                                                                                \
-    };                                                                                   \
-    } /* toml */
-
-#endif// TOML11_WITHOUT_DEFINE_NON_INTRUSIVE
-
-#endif// TOML11_MACROS_HPP
diff --git a/src/toml11/toml/parser.hpp b/src/toml11/toml/parser.hpp
deleted file mode 100644
index e31179918..000000000
--- a/src/toml11/toml/parser.hpp
+++ /dev/null
@@ -1,2364 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_PARSER_HPP
-#define TOML11_PARSER_HPP
-#include <cstring>
-#include <fstream>
-#include <sstream>
-
-#include "combinator.hpp"
-#include "lexer.hpp"
-#include "region.hpp"
-#include "result.hpp"
-#include "types.hpp"
-#include "value.hpp"
-
-#ifndef TOML11_DISABLE_STD_FILESYSTEM
-#ifdef __cpp_lib_filesystem
-#if __has_include(<filesystem>)
-#define TOML11_HAS_STD_FILESYSTEM
-#include <filesystem>
-#endif // has_include(<string_view>)
-#endif // __cpp_lib_filesystem
-#endif // TOML11_DISABLE_STD_FILESYSTEM
-
-namespace toml
-{
-namespace detail
-{
-
-inline result<std::pair<boolean, region>, std::string>
-parse_boolean(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_boolean::invoke(loc))
-    {
-        const auto reg = token.unwrap();
-        if     (reg.str() == "true")  {return ok(std::make_pair(true,  reg));}
-        else if(reg.str() == "false") {return ok(std::make_pair(false, reg));}
-        else // internal error.
-        {
-            throw internal_error(format_underline(
-                "toml::parse_boolean: internal error",
-                {{source_location(reg), "invalid token"}}),
-                source_location(reg));
-        }
-    }
-    loc.reset(first); //rollback
-    return err(format_underline("toml::parse_boolean: ",
-               {{source_location(loc), "the next token is not a boolean"}}));
-}
-
-inline result<std::pair<integer, region>, std::string>
-parse_binary_integer(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_bin_int::invoke(loc))
-    {
-        auto str = token.unwrap().str();
-        assert(str.size() > 2); // minimum -> 0b1
-        integer retval(0), base(1);
-        for(auto i(str.rbegin()), e(str.rend() - 2); i!=e; ++i)
-        {
-            if     (*i == '1'){retval += base; base *= 2;}
-            else if(*i == '0'){base *= 2;}
-            else if(*i == '_'){/* do nothing. */}
-            else // internal error.
-            {
-                throw internal_error(format_underline(
-                    "toml::parse_integer: internal error",
-                    {{source_location(token.unwrap()), "invalid token"}}),
-                    source_location(loc));
-            }
-        }
-        return ok(std::make_pair(retval, token.unwrap()));
-    }
-    loc.reset(first);
-    return err(format_underline("toml::parse_binary_integer:",
-               {{source_location(loc), "the next token is not an integer"}}));
-}
-
-inline result<std::pair<integer, region>, std::string>
-parse_octal_integer(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_oct_int::invoke(loc))
-    {
-        auto str = token.unwrap().str();
-        str.erase(std::remove(str.begin(), str.end(), '_'), str.end());
-        str.erase(str.begin()); str.erase(str.begin()); // remove `0o` prefix
-
-        std::istringstream iss(str);
-        integer retval(0);
-        iss >> std::oct >> retval;
-        return ok(std::make_pair(retval, token.unwrap()));
-    }
-    loc.reset(first);
-    return err(format_underline("toml::parse_octal_integer:",
-               {{source_location(loc), "the next token is not an integer"}}));
-}
-
-inline result<std::pair<integer, region>, std::string>
-parse_hexadecimal_integer(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_hex_int::invoke(loc))
-    {
-        auto str = token.unwrap().str();
-        str.erase(std::remove(str.begin(), str.end(), '_'), str.end());
-        str.erase(str.begin()); str.erase(str.begin()); // remove `0x` prefix
-
-        std::istringstream iss(str);
-        integer retval(0);
-        iss >> std::hex >> retval;
-        return ok(std::make_pair(retval, token.unwrap()));
-    }
-    loc.reset(first);
-    return err(format_underline("toml::parse_hexadecimal_integer",
-               {{source_location(loc), "the next token is not an integer"}}));
-}
-
-inline result<std::pair<integer, region>, std::string>
-parse_integer(location& loc)
-{
-    const auto first = loc.iter();
-    if(first != loc.end() && *first == '0')
-    {
-        const auto second = std::next(first);
-        if(second == loc.end()) // the token is just zero.
-        {
-            loc.advance();
-            return ok(std::make_pair(0, region(loc, first, second)));
-        }
-
-        if(*second == 'b') {return parse_binary_integer     (loc);} // 0b1100
-        if(*second == 'o') {return parse_octal_integer      (loc);} // 0o775
-        if(*second == 'x') {return parse_hexadecimal_integer(loc);} // 0xC0FFEE
-
-        if(std::isdigit(*second))
-        {
-            return err(format_underline("toml::parse_integer: "
-                "leading zero in an Integer is not allowed.",
-                {{source_location(loc), "leading zero"}}));
-        }
-        else if(std::isalpha(*second))
-        {
-             return err(format_underline("toml::parse_integer: "
-                "unknown integer prefix appeared.",
-                {{source_location(loc), "none of 0x, 0o, 0b"}}));
-        }
-    }
-
-    if(const auto token = lex_dec_int::invoke(loc))
-    {
-        auto str = token.unwrap().str();
-        str.erase(std::remove(str.begin(), str.end(), '_'), str.end());
-
-        std::istringstream iss(str);
-        integer retval(0);
-        iss >> retval;
-        return ok(std::make_pair(retval, token.unwrap()));
-    }
-    loc.reset(first);
-    return err(format_underline("toml::parse_integer: ",
-               {{source_location(loc), "the next token is not an integer"}}));
-}
-
-inline result<std::pair<floating, region>, std::string>
-parse_floating(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_float::invoke(loc))
-    {
-        auto str = token.unwrap().str();
-        if(str == "inf" || str == "+inf")
-        {
-            if(std::numeric_limits<floating>::has_infinity)
-            {
-                return ok(std::make_pair(
-                    std::numeric_limits<floating>::infinity(), token.unwrap()));
-            }
-            else
-            {
-                throw std::domain_error("toml::parse_floating: inf value found"
-                    " but the current environment does not support inf. Please"
-                    " make sure that the floating-point implementation conforms"
-                    " IEEE 754/ISO 60559 international standard.");
-            }
-        }
-        else if(str == "-inf")
-        {
-            if(std::numeric_limits<floating>::has_infinity)
-            {
-                return ok(std::make_pair(
-                    -std::numeric_limits<floating>::infinity(), token.unwrap()));
-            }
-            else
-            {
-                throw std::domain_error("toml::parse_floating: inf value found"
-                    " but the current environment does not support inf. Please"
-                    " make sure that the floating-point implementation conforms"
-                    " IEEE 754/ISO 60559 international standard.");
-            }
-        }
-        else if(str == "nan" || str == "+nan")
-        {
-            if(std::numeric_limits<floating>::has_quiet_NaN)
-            {
-                return ok(std::make_pair(
-                    std::numeric_limits<floating>::quiet_NaN(), token.unwrap()));
-            }
-            else if(std::numeric_limits<floating>::has_signaling_NaN)
-            {
-                return ok(std::make_pair(
-                    std::numeric_limits<floating>::signaling_NaN(), token.unwrap()));
-            }
-            else
-            {
-                throw std::domain_error("toml::parse_floating: NaN value found"
-                    " but the current environment does not support NaN. Please"
-                    " make sure that the floating-point implementation conforms"
-                    " IEEE 754/ISO 60559 international standard.");
-            }
-        }
-        else if(str == "-nan")
-        {
-            if(std::numeric_limits<floating>::has_quiet_NaN)
-            {
-                return ok(std::make_pair(
-                    -std::numeric_limits<floating>::quiet_NaN(), token.unwrap()));
-            }
-            else if(std::numeric_limits<floating>::has_signaling_NaN)
-            {
-                return ok(std::make_pair(
-                    -std::numeric_limits<floating>::signaling_NaN(), token.unwrap()));
-            }
-            else
-            {
-                throw std::domain_error("toml::parse_floating: NaN value found"
-                    " but the current environment does not support NaN. Please"
-                    " make sure that the floating-point implementation conforms"
-                    " IEEE 754/ISO 60559 international standard.");
-            }
-        }
-        str.erase(std::remove(str.begin(), str.end(), '_'), str.end());
-        std::istringstream iss(str);
-        floating v(0.0);
-        iss >> v;
-        return ok(std::make_pair(v, token.unwrap()));
-    }
-    loc.reset(first);
-    return err(format_underline("toml::parse_floating: ",
-               {{source_location(loc), "the next token is not a float"}}));
-}
-
-inline std::string read_utf8_codepoint(const region& reg, const location& loc)
-{
-    const auto str = reg.str().substr(1);
-    std::uint_least32_t codepoint;
-    std::istringstream iss(str);
-    iss >> std::hex >> codepoint;
-
-    const auto to_char = [](const std::uint_least32_t i) noexcept -> char {
-        const auto uc = static_cast<unsigned char>(i);
-        return *reinterpret_cast<const char*>(std::addressof(uc));
-    };
-
-    std::string character;
-    if(codepoint < 0x80) // U+0000 ... U+0079 ; just an ASCII.
-    {
-        character += static_cast<char>(codepoint);
-    }
-    else if(codepoint < 0x800) //U+0080 ... U+07FF
-    {
-        // 110yyyyx 10xxxxxx; 0x3f == 0b0011'1111
-        character += to_char(0xC0| codepoint >> 6);
-        character += to_char(0x80|(codepoint & 0x3F));
-    }
-    else if(codepoint < 0x10000) // U+0800...U+FFFF
-    {
-        if(0xD800 <= codepoint && codepoint <= 0xDFFF)
-        {
-            throw syntax_error(format_underline(
-                "toml::read_utf8_codepoint: codepoints in the range "
-                "[0xD800, 0xDFFF] are not valid UTF-8.", {{
-                    source_location(loc), "not a valid UTF-8 codepoint"
-                }}), source_location(loc));
-        }
-        assert(codepoint < 0xD800 || 0xDFFF < codepoint);
-        // 1110yyyy 10yxxxxx 10xxxxxx
-        character += to_char(0xE0| codepoint >> 12);
-        character += to_char(0x80|(codepoint >> 6 & 0x3F));
-        character += to_char(0x80|(codepoint      & 0x3F));
-    }
-    else if(codepoint < 0x110000) // U+010000 ... U+10FFFF
-    {
-        // 11110yyy 10yyxxxx 10xxxxxx 10xxxxxx
-        character += to_char(0xF0| codepoint >> 18);
-        character += to_char(0x80|(codepoint >> 12 & 0x3F));
-        character += to_char(0x80|(codepoint >> 6  & 0x3F));
-        character += to_char(0x80|(codepoint       & 0x3F));
-    }
-    else // out of UTF-8 region
-    {
-        throw syntax_error(format_underline("toml::read_utf8_codepoint:"
-            " input codepoint is too large.",
-            {{source_location(loc), "should be in [0x00..0x10FFFF]"}}),
-            source_location(loc));
-    }
-    return character;
-}
-
-inline result<std::string, std::string> parse_escape_sequence(location& loc)
-{
-    const auto first = loc.iter();
-    if(first == loc.end() || *first != '\\')
-    {
-        return err(format_underline("toml::parse_escape_sequence: ", {{
-            source_location(loc), "the next token is not a backslash \"\\\""}}));
-    }
-    loc.advance();
-    switch(*loc.iter())
-    {
-        case '\\':{loc.advance(); return ok(std::string("\\"));}
-        case '"' :{loc.advance(); return ok(std::string("\""));}
-        case 'b' :{loc.advance(); return ok(std::string("\b"));}
-        case 't' :{loc.advance(); return ok(std::string("\t"));}
-        case 'n' :{loc.advance(); return ok(std::string("\n"));}
-        case 'f' :{loc.advance(); return ok(std::string("\f"));}
-        case 'r' :{loc.advance(); return ok(std::string("\r"));}
-        case 'u' :
-        {
-            if(const auto token = lex_escape_unicode_short::invoke(loc))
-            {
-                return ok(read_utf8_codepoint(token.unwrap(), loc));
-            }
-            else
-            {
-                return err(format_underline("parse_escape_sequence: "
-                           "invalid token found in UTF-8 codepoint uXXXX.",
-                           {{source_location(loc), "here"}}));
-            }
-        }
-        case 'U':
-        {
-            if(const auto token = lex_escape_unicode_long::invoke(loc))
-            {
-                return ok(read_utf8_codepoint(token.unwrap(), loc));
-            }
-            else
-            {
-                return err(format_underline("parse_escape_sequence: "
-                           "invalid token found in UTF-8 codepoint Uxxxxxxxx",
-                           {{source_location(loc), "here"}}));
-            }
-        }
-    }
-
-    const auto msg = format_underline("parse_escape_sequence: "
-           "unknown escape sequence appeared.", {{source_location(loc),
-           "escape sequence is one of \\, \", b, t, n, f, r, uxxxx, Uxxxxxxxx"}},
-           /* Hints = */{"if you want to write backslash as just one backslash, "
-           "use literal string like: regex    = '<\\i\\c*\\s*>'"});
-    loc.reset(first);
-    return err(msg);
-}
-
-inline std::ptrdiff_t check_utf8_validity(const std::string& reg)
-{
-    location loc("tmp", reg);
-    const auto u8 = repeat<lex_utf8_code, unlimited>::invoke(loc);
-    if(!u8 || loc.iter() != loc.end())
-    {
-        const auto error_location = std::distance(loc.begin(), loc.iter());
-        assert(0 <= error_location);
-        return error_location;
-    }
-    return -1;
-}
-
-inline result<std::pair<toml::string, region>, std::string>
-parse_ml_basic_string(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_ml_basic_string::invoke(loc))
-    {
-        auto inner_loc = loc;
-        inner_loc.reset(first);
-
-        std::string retval;
-        retval.reserve(token.unwrap().size());
-
-        auto delim = lex_ml_basic_string_open::invoke(inner_loc);
-        if(!delim)
-        {
-            throw internal_error(format_underline(
-                "parse_ml_basic_string: invalid token",
-                {{source_location(inner_loc), "should be \"\"\""}}),
-                source_location(inner_loc));
-        }
-        // immediate newline is ignored (if exists)
-        /* discard return value */ lex_newline::invoke(inner_loc);
-
-        delim = none();
-        while(!delim)
-        {
-            using lex_unescaped_seq = repeat<
-                either<lex_ml_basic_unescaped, lex_newline>, unlimited>;
-            if(auto unescaped = lex_unescaped_seq::invoke(inner_loc))
-            {
-                retval += unescaped.unwrap().str();
-            }
-            if(auto escaped = parse_escape_sequence(inner_loc))
-            {
-                retval += escaped.unwrap();
-            }
-            if(auto esc_nl = lex_ml_basic_escaped_newline::invoke(inner_loc))
-            {
-                // ignore newline after escape until next non-ws char
-            }
-            if(inner_loc.iter() == inner_loc.end())
-            {
-                throw internal_error(format_underline(
-                    "parse_ml_basic_string: unexpected end of region",
-                    {{source_location(inner_loc), "not sufficient token"}}),
-                    source_location(inner_loc));
-            }
-            delim = lex_ml_basic_string_close::invoke(inner_loc);
-        }
-        // `lex_ml_basic_string_close` allows 3 to 5 `"`s to allow 1 or 2 `"`s
-        // at just before the delimiter. Here, we need to attach `"`s at the
-        // end of the string body, if it exists.
-        // For detail, see the definition of `lex_ml_basic_string_close`.
-        assert(std::all_of(delim.unwrap().first(), delim.unwrap().last(),
-                           [](const char c) noexcept {return c == '\"';}));
-        switch(delim.unwrap().size())
-        {
-            case 3: {break;}
-            case 4: {retval += "\"";  break;}
-            case 5: {retval += "\"\""; break;}
-            default:
-            {
-                throw internal_error(format_underline(
-                    "parse_ml_basic_string: closing delimiter has invalid length",
-                    {{source_location(inner_loc), "end of this"}}),
-                    source_location(inner_loc));
-            }
-        }
-
-        const auto err_loc = check_utf8_validity(token.unwrap().str());
-        if(err_loc == -1)
-        {
-            return ok(std::make_pair(toml::string(retval), token.unwrap()));
-        }
-        else
-        {
-            inner_loc.reset(first);
-            inner_loc.advance(err_loc);
-            throw syntax_error(format_underline(
-                "parse_ml_basic_string: invalid utf8 sequence found",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-    }
-    else
-    {
-        loc.reset(first);
-        return err(format_underline("toml::parse_ml_basic_string: "
-                   "the next token is not a valid multiline string",
-                   {{source_location(loc), "here"}}));
-    }
-}
-
-inline result<std::pair<toml::string, region>, std::string>
-parse_basic_string(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_basic_string::invoke(loc))
-    {
-        auto inner_loc = loc;
-        inner_loc.reset(first);
-
-        auto quot = lex_quotation_mark::invoke(inner_loc);
-        if(!quot)
-        {
-            throw internal_error(format_underline("parse_basic_string: "
-                "invalid token", {{source_location(inner_loc), "should be \""}}),
-                source_location(inner_loc));
-        }
-
-        std::string retval;
-        retval.reserve(token.unwrap().size());
-
-        quot = none();
-        while(!quot)
-        {
-            using lex_unescaped_seq = repeat<lex_basic_unescaped, unlimited>;
-            if(auto unescaped = lex_unescaped_seq::invoke(inner_loc))
-            {
-                retval += unescaped.unwrap().str();
-            }
-            if(auto escaped = parse_escape_sequence(inner_loc))
-            {
-                retval += escaped.unwrap();
-            }
-            if(inner_loc.iter() == inner_loc.end())
-            {
-                throw internal_error(format_underline(
-                    "parse_basic_string: unexpected end of region",
-                    {{source_location(inner_loc), "not sufficient token"}}),
-                    source_location(inner_loc));
-            }
-            quot = lex_quotation_mark::invoke(inner_loc);
-        }
-
-        const auto err_loc = check_utf8_validity(token.unwrap().str());
-        if(err_loc == -1)
-        {
-            return ok(std::make_pair(toml::string(retval), token.unwrap()));
-        }
-        else
-        {
-            inner_loc.reset(first);
-            inner_loc.advance(err_loc);
-            throw syntax_error(format_underline(
-                "parse_ml_basic_string: invalid utf8 sequence found",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-    }
-    else
-    {
-        loc.reset(first); // rollback
-        return err(format_underline("toml::parse_basic_string: "
-                   "the next token is not a valid string",
-                   {{source_location(loc), "here"}}));
-    }
-}
-
-inline result<std::pair<toml::string, region>, std::string>
-parse_ml_literal_string(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_ml_literal_string::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto open = lex_ml_literal_string_open::invoke(inner_loc);
-        if(!open)
-        {
-            throw internal_error(format_underline(
-                "parse_ml_literal_string: invalid token",
-                {{source_location(inner_loc), "should be '''"}}),
-                source_location(inner_loc));
-        }
-        // immediate newline is ignored (if exists)
-        /* discard return value */ lex_newline::invoke(inner_loc);
-
-        const auto body = lex_ml_literal_body::invoke(inner_loc);
-
-        const auto close = lex_ml_literal_string_close::invoke(inner_loc);
-        if(!close)
-        {
-            throw internal_error(format_underline(
-                "parse_ml_literal_string: invalid token",
-                {{source_location(inner_loc), "should be '''"}}),
-                source_location(inner_loc));
-        }
-        // `lex_ml_literal_string_close` allows 3 to 5 `'`s to allow 1 or 2 `'`s
-        // at just before the delimiter. Here, we need to attach `'`s at the
-        // end of the string body, if it exists.
-        // For detail, see the definition of `lex_ml_basic_string_close`.
-
-        std::string retval = body.unwrap().str();
-        assert(std::all_of(close.unwrap().first(), close.unwrap().last(),
-                           [](const char c) noexcept {return c == '\'';}));
-        switch(close.unwrap().size())
-        {
-            case 3: {break;}
-            case 4: {retval += "'";  break;}
-            case 5: {retval += "''"; break;}
-            default:
-            {
-                throw internal_error(format_underline(
-                    "parse_ml_literal_string: closing delimiter has invalid length",
-                    {{source_location(inner_loc), "end of this"}}),
-                    source_location(inner_loc));
-            }
-        }
-
-        const auto err_loc = check_utf8_validity(token.unwrap().str());
-        if(err_loc == -1)
-        {
-            return ok(std::make_pair(toml::string(retval, toml::string_t::literal),
-                                     token.unwrap()));
-        }
-        else
-        {
-            inner_loc.reset(first);
-            inner_loc.advance(err_loc);
-            throw syntax_error(format_underline(
-                "parse_ml_basic_string: invalid utf8 sequence found",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-    }
-    else
-    {
-        loc.reset(first); // rollback
-        return err(format_underline("toml::parse_ml_literal_string: "
-                   "the next token is not a valid multiline literal string",
-                   {{source_location(loc), "here"}}));
-    }
-}
-
-inline result<std::pair<toml::string, region>, std::string>
-parse_literal_string(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_literal_string::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto open = lex_apostrophe::invoke(inner_loc);
-        if(!open)
-        {
-            throw internal_error(format_underline(
-                "parse_literal_string: invalid token",
-                {{source_location(inner_loc), "should be '"}}),
-                source_location(inner_loc));
-        }
-
-        const auto body = repeat<lex_literal_char, unlimited>::invoke(inner_loc);
-
-        const auto close = lex_apostrophe::invoke(inner_loc);
-        if(!close)
-        {
-            throw internal_error(format_underline(
-                "parse_literal_string: invalid token",
-                {{source_location(inner_loc), "should be '"}}),
-                source_location(inner_loc));
-        }
-
-        const auto err_loc = check_utf8_validity(token.unwrap().str());
-        if(err_loc == -1)
-        {
-            return ok(std::make_pair(
-                      toml::string(body.unwrap().str(), toml::string_t::literal),
-                      token.unwrap()));
-        }
-        else
-        {
-            inner_loc.reset(first);
-            inner_loc.advance(err_loc);
-            throw syntax_error(format_underline(
-                "parse_ml_basic_string: invalid utf8 sequence found",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-    }
-    else
-    {
-        loc.reset(first); // rollback
-        return err(format_underline("toml::parse_literal_string: "
-                   "the next token is not a valid literal string",
-                   {{source_location(loc), "here"}}));
-    }
-}
-
-inline result<std::pair<toml::string, region>, std::string>
-parse_string(location& loc)
-{
-    if(loc.iter() != loc.end() && *(loc.iter()) == '"')
-    {
-        if(loc.iter() + 1 != loc.end() && *(loc.iter() + 1) == '"' &&
-           loc.iter() + 2 != loc.end() && *(loc.iter() + 2) == '"')
-        {
-            return parse_ml_basic_string(loc);
-        }
-        else
-        {
-            return parse_basic_string(loc);
-        }
-    }
-    else if(loc.iter() != loc.end() && *(loc.iter()) == '\'')
-    {
-        if(loc.iter() + 1 != loc.end() && *(loc.iter() + 1) == '\'' &&
-           loc.iter() + 2 != loc.end() && *(loc.iter() + 2) == '\'')
-        {
-            return parse_ml_literal_string(loc);
-        }
-        else
-        {
-            return parse_literal_string(loc);
-        }
-    }
-    return err(format_underline("toml::parse_string: ",
-                {{source_location(loc), "the next token is not a string"}}));
-}
-
-inline result<std::pair<local_date, region>, std::string>
-parse_local_date(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_local_date::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto y = lex_date_fullyear::invoke(inner_loc);
-        if(!y || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != '-')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_inner_local_date: invalid year format",
-                {{source_location(inner_loc), "should be `-`"}}),
-                source_location(inner_loc));
-        }
-        inner_loc.advance();
-        const auto m = lex_date_month::invoke(inner_loc);
-        if(!m || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != '-')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_date: invalid month format",
-                {{source_location(inner_loc), "should be `-`"}}),
-                source_location(inner_loc));
-        }
-        inner_loc.advance();
-        const auto d = lex_date_mday::invoke(inner_loc);
-        if(!d)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_date: invalid day format",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-
-        const auto year  = static_cast<std::int16_t>(from_string<int>(y.unwrap().str(), 0));
-        const auto month = static_cast<std::int8_t >(from_string<int>(m.unwrap().str(), 0));
-        const auto day   = static_cast<std::int8_t >(from_string<int>(d.unwrap().str(), 0));
-
-        // We briefly check whether the input date is valid or not. But here, we
-        // only check if the RFC3339 compliance.
-        //     Actually there are several special date that does not exist,
-        // because of historical reasons, such as 1582/10/5-1582/10/14 (only in
-        // several countries). But here, we do not care about such a complicated
-        // rule. It makes the code complicated and there is only low probability
-        // that such a specific date is needed in practice. If someone need to
-        // validate date accurately, that means that the one need a specialized
-        // library for their purpose in a different layer.
-        {
-            const bool is_leap = (year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0));
-            const auto max_day = (month == 2) ? (is_leap ? 29 : 28) :
-                ((month == 4 || month == 6 || month == 9 || month == 11) ? 30 : 31);
-
-            if((month < 1 || 12 < month) || (day < 1 || max_day < day))
-            {
-                throw syntax_error(format_underline("toml::parse_date: "
-                    "invalid date: it does not conform RFC3339.", {{
-                    source_location(loc), "month should be 01-12, day should be"
-                    " 01-28,29,30,31, depending on month/year."
-                    }}), source_location(inner_loc));
-            }
-        }
-        return ok(std::make_pair(local_date(year, static_cast<month_t>(month - 1), day),
-                                 token.unwrap()));
-    }
-    else
-    {
-        loc.reset(first);
-        return err(format_underline("toml::parse_local_date: ",
-            {{source_location(loc), "the next token is not a local_date"}}));
-    }
-}
-
-inline result<std::pair<local_time, region>, std::string>
-parse_local_time(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_local_time::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto h = lex_time_hour::invoke(inner_loc);
-        if(!h || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != ':')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_time: invalid year format",
-                {{source_location(inner_loc), "should be `:`"}}),
-                source_location(inner_loc));
-        }
-        inner_loc.advance();
-        const auto m = lex_time_minute::invoke(inner_loc);
-        if(!m || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != ':')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_time: invalid month format",
-                {{source_location(inner_loc), "should be `:`"}}),
-                source_location(inner_loc));
-        }
-        inner_loc.advance();
-        const auto s = lex_time_second::invoke(inner_loc);
-        if(!s)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_time: invalid second format",
-                {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-        }
-
-        const int hour   = from_string<int>(h.unwrap().str(), 0);
-        const int minute = from_string<int>(m.unwrap().str(), 0);
-        const int second = from_string<int>(s.unwrap().str(), 0);
-
-        if((hour   < 0 || 23 < hour) || (minute < 0 || 59 < minute) ||
-           (second < 0 || 60 < second)) // it may be leap second
-        {
-            throw syntax_error(format_underline("toml::parse_time: "
-                "invalid time: it does not conform RFC3339.", {{
-                source_location(loc), "hour should be 00-23, minute should be"
-                " 00-59, second should be 00-60 (depending on the leap"
-                " second rules.)"}}), source_location(inner_loc));
-        }
-
-        local_time time(hour, minute, second, 0, 0);
-
-        const auto before_secfrac = inner_loc.iter();
-        if(const auto secfrac = lex_time_secfrac::invoke(inner_loc))
-        {
-            auto sf = secfrac.unwrap().str();
-            sf.erase(sf.begin()); // sf.front() == '.'
-            switch(sf.size() % 3)
-            {
-                case 2:  sf += '0';  break;
-                case 1:  sf += "00"; break;
-                case 0:  break;
-                default: break;
-            }
-            if(sf.size() >= 9)
-            {
-                time.millisecond = from_string<std::uint16_t>(sf.substr(0, 3), 0u);
-                time.microsecond = from_string<std::uint16_t>(sf.substr(3, 3), 0u);
-                time.nanosecond  = from_string<std::uint16_t>(sf.substr(6, 3), 0u);
-            }
-            else if(sf.size() >= 6)
-            {
-                time.millisecond = from_string<std::uint16_t>(sf.substr(0, 3), 0u);
-                time.microsecond = from_string<std::uint16_t>(sf.substr(3, 3), 0u);
-            }
-            else if(sf.size() >= 3)
-            {
-                time.millisecond = from_string<std::uint16_t>(sf, 0u);
-                time.microsecond = 0u;
-            }
-        }
-        else
-        {
-            if(before_secfrac != inner_loc.iter())
-            {
-                throw internal_error(format_underline(
-                    "toml::parse_local_time: invalid subsecond format",
-                    {{source_location(inner_loc), "here"}}),
-                source_location(inner_loc));
-            }
-        }
-        return ok(std::make_pair(time, token.unwrap()));
-    }
-    else
-    {
-        loc.reset(first);
-        return err(format_underline("toml::parse_local_time: ",
-            {{source_location(loc), "the next token is not a local_time"}}));
-    }
-}
-
-inline result<std::pair<local_datetime, region>, std::string>
-parse_local_datetime(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_local_date_time::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-        const auto date = parse_local_date(inner_loc);
-        if(!date || inner_loc.iter() == inner_loc.end())
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_datetime: invalid datetime format",
-                {{source_location(inner_loc), "date, not datetime"}}),
-                source_location(inner_loc));
-        }
-        const char delim = *(inner_loc.iter());
-        if(delim != 'T' && delim != 't' && delim != ' ')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_datetime: invalid datetime format",
-                {{source_location(inner_loc), "should be `T` or ` ` (space)"}}),
-                source_location(inner_loc));
-        }
-        inner_loc.advance();
-        const auto time = parse_local_time(inner_loc);
-        if(!time)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_local_datetime: invalid datetime format",
-                {{source_location(inner_loc), "invalid time format"}}),
-                source_location(inner_loc));
-        }
-        return ok(std::make_pair(
-            local_datetime(date.unwrap().first, time.unwrap().first),
-            token.unwrap()));
-    }
-    else
-    {
-        loc.reset(first);
-        return err(format_underline("toml::parse_local_datetime: ",
-            {{source_location(loc), "the next token is not a local_datetime"}}));
-    }
-}
-
-inline result<std::pair<offset_datetime, region>, std::string>
-parse_offset_datetime(location& loc)
-{
-    const auto first = loc.iter();
-    if(const auto token = lex_offset_date_time::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-        const auto datetime = parse_local_datetime(inner_loc);
-        if(!datetime || inner_loc.iter() == inner_loc.end())
-        {
-            throw internal_error(format_underline(
-                "toml::parse_offset_datetime: invalid datetime format",
-                {{source_location(inner_loc), "date, not datetime"}}),
-                source_location(inner_loc));
-        }
-        time_offset offset(0, 0);
-        if(const auto ofs = lex_time_numoffset::invoke(inner_loc))
-        {
-            const auto str = ofs.unwrap().str();
-
-            const auto hour   = from_string<int>(str.substr(1,2), 0);
-            const auto minute = from_string<int>(str.substr(4,2), 0);
-
-            if((hour < 0 || 23 < hour) || (minute < 0 || 59 < minute))
-            {
-                throw syntax_error(format_underline("toml::parse_offset_datetime: "
-                    "invalid offset: it does not conform RFC3339.", {{
-                    source_location(loc), "month should be 01-12, day should be"
-                    " 01-28,29,30,31, depending on month/year."
-                    }}), source_location(inner_loc));
-            }
-
-            if(str.front() == '+')
-            {
-                offset = time_offset(hour, minute);
-            }
-            else
-            {
-                offset = time_offset(-hour, -minute);
-            }
-        }
-        else if(*inner_loc.iter() != 'Z' && *inner_loc.iter() != 'z')
-        {
-            throw internal_error(format_underline(
-                "toml::parse_offset_datetime: invalid datetime format",
-                {{source_location(inner_loc), "should be `Z` or `+HH:MM`"}}),
-                source_location(inner_loc));
-        }
-        return ok(std::make_pair(offset_datetime(datetime.unwrap().first, offset),
-                                 token.unwrap()));
-    }
-    else
-    {
-        loc.reset(first);
-        return err(format_underline("toml::parse_offset_datetime: ",
-            {{source_location(loc), "the next token is not a offset_datetime"}}));
-    }
-}
-
-inline result<std::pair<key, region>, std::string>
-parse_simple_key(location& loc)
-{
-    if(const auto bstr = parse_basic_string(loc))
-    {
-        return ok(std::make_pair(bstr.unwrap().first.str, bstr.unwrap().second));
-    }
-    if(const auto lstr = parse_literal_string(loc))
-    {
-        return ok(std::make_pair(lstr.unwrap().first.str, lstr.unwrap().second));
-    }
-    if(const auto bare = lex_unquoted_key::invoke(loc))
-    {
-        const auto reg = bare.unwrap();
-        return ok(std::make_pair(reg.str(), reg));
-    }
-    return err(format_underline("toml::parse_simple_key: ",
-            {{source_location(loc), "the next token is not a simple key"}}));
-}
-
-// dotted key become vector of keys
-inline result<std::pair<std::vector<key>, region>, std::string>
-parse_key(location& loc)
-{
-    const auto first = loc.iter();
-    // dotted key -> `foo.bar.baz` where several single keys are chained by
-    // dots. Whitespaces between keys and dots are allowed.
-    if(const auto token = lex_dotted_key::invoke(loc))
-    {
-        const auto reg = token.unwrap();
-        location inner_loc(loc.name(), reg.str());
-        std::vector<key> keys;
-
-        while(inner_loc.iter() != inner_loc.end())
-        {
-            lex_ws::invoke(inner_loc);
-            if(const auto k = parse_simple_key(inner_loc))
-            {
-                keys.push_back(k.unwrap().first);
-            }
-            else
-            {
-                throw internal_error(format_underline(
-                    "toml::detail::parse_key: dotted key contains invalid key",
-                    {{source_location(inner_loc), k.unwrap_err()}}),
-                    source_location(inner_loc));
-            }
-
-            lex_ws::invoke(inner_loc);
-            if(inner_loc.iter() == inner_loc.end())
-            {
-                break;
-            }
-            else if(*inner_loc.iter() == '.')
-            {
-                inner_loc.advance(); // to skip `.`
-            }
-            else
-            {
-                throw internal_error(format_underline("toml::parse_key: "
-                    "dotted key contains invalid key ",
-                    {{source_location(inner_loc), "should be `.`"}}),
-                    source_location(inner_loc));
-            }
-        }
-        return ok(std::make_pair(keys, reg));
-    }
-    loc.reset(first);
-
-    // simple_key: a single (basic_string|literal_string|bare key)
-    if(const auto smpl = parse_simple_key(loc))
-    {
-        return ok(std::make_pair(std::vector<key>(1, smpl.unwrap().first),
-                                 smpl.unwrap().second));
-    }
-    return err(format_underline("toml::parse_key: an invalid key appeared.",
-                {{source_location(loc), "is not a valid key"}}, {
-                "bare keys  : non-empty strings composed only of [A-Za-z0-9_-].",
-                "quoted keys: same as \"basic strings\" or 'literal strings'.",
-                "dotted keys: sequence of bare or quoted keys joined with a dot."
-                }));
-}
-
-// forward-decl to implement parse_array and parse_table
-template<typename Value>
-result<Value, std::string> parse_value(location&);
-
-template<typename Value>
-result<std::pair<typename Value::array_type, region>, std::string>
-parse_array(location& loc)
-{
-    using value_type = Value;
-    using array_type = typename value_type::array_type;
-
-    const auto first = loc.iter();
-    if(loc.iter() == loc.end())
-    {
-        return err("toml::parse_array: input is empty");
-    }
-    if(*loc.iter() != '[')
-    {
-        return err("toml::parse_array: token is not an array");
-    }
-    loc.advance();
-
-    using lex_ws_comment_newline = repeat<
-        either<lex_wschar, lex_newline, lex_comment>, unlimited>;
-
-    array_type retval;
-    while(loc.iter() != loc.end())
-    {
-        lex_ws_comment_newline::invoke(loc); // skip
-
-        if(loc.iter() != loc.end() && *loc.iter() == ']')
-        {
-            loc.advance(); // skip ']'
-            return ok(std::make_pair(retval,
-                      region(loc, first, loc.iter())));
-        }
-
-        if(auto val = parse_value<value_type>(loc))
-        {
-            // After TOML v1.0.0-rc.1, array becomes to be able to have values
-            // with different types. So here we will omit this by default.
-            //
-            // But some of the test-suite checks if the parser accepts a hetero-
-            // geneous arrays, so we keep this for a while.
-#ifdef TOML11_DISALLOW_HETEROGENEOUS_ARRAYS
-            if(!retval.empty() && retval.front().type() != val.as_ok().type())
-            {
-                auto array_start_loc = loc;
-                array_start_loc.reset(first);
-
-                throw syntax_error(format_underline("toml::parse_array: "
-                    "type of elements should be the same each other.", {
-                        {source_location(array_start_loc), "array starts here"},
-                        {
-                            retval.front().location(),
-                            "value has type " + stringize(retval.front().type())
-                        },
-                        {
-                            val.unwrap().location(),
-                            "value has different type, " + stringize(val.unwrap().type())
-                        }
-                    }), source_location(loc));
-            }
-#endif
-            retval.push_back(std::move(val.unwrap()));
-        }
-        else
-        {
-            auto array_start_loc = loc;
-            array_start_loc.reset(first);
-
-            throw syntax_error(format_underline("toml::parse_array: "
-                "value having invalid format appeared in an array", {
-                    {source_location(array_start_loc), "array starts here"},
-                    {source_location(loc), "it is not a valid value."}
-                }), source_location(loc));
-        }
-
-        using lex_array_separator = sequence<maybe<lex_ws_comment_newline>, character<','>>;
-        const auto sp = lex_array_separator::invoke(loc);
-        if(!sp)
-        {
-            lex_ws_comment_newline::invoke(loc);
-            if(loc.iter() != loc.end() && *loc.iter() == ']')
-            {
-                loc.advance(); // skip ']'
-                return ok(std::make_pair(retval,
-                          region(loc, first, loc.iter())));
-            }
-            else
-            {
-                auto array_start_loc = loc;
-                array_start_loc.reset(first);
-
-                throw syntax_error(format_underline("toml::parse_array:"
-                    " missing array separator `,` after a value", {
-                        {source_location(array_start_loc), "array starts here"},
-                        {source_location(loc),             "should be `,`"}
-                    }), source_location(loc));
-            }
-        }
-    }
-    loc.reset(first);
-    throw syntax_error(format_underline("toml::parse_array: "
-            "array did not closed by `]`",
-            {{source_location(loc), "should be closed"}}),
-            source_location(loc));
-}
-
-template<typename Value>
-result<std::pair<std::pair<std::vector<key>, region>, Value>, std::string>
-parse_key_value_pair(location& loc)
-{
-    using value_type = Value;
-
-    const auto first = loc.iter();
-    auto key_reg = parse_key(loc);
-    if(!key_reg)
-    {
-        std::string msg = std::move(key_reg.unwrap_err());
-        // if the next token is keyvalue-separator, it means that there are no
-        // key. then we need to show error as "empty key is not allowed".
-        if(const auto keyval_sep = lex_keyval_sep::invoke(loc))
-        {
-            loc.reset(first);
-            msg = format_underline("toml::parse_key_value_pair: "
-                "empty key is not allowed.",
-                {{source_location(loc), "key expected before '='"}});
-        }
-        return err(std::move(msg));
-    }
-
-    const auto kvsp = lex_keyval_sep::invoke(loc);
-    if(!kvsp)
-    {
-        std::string msg;
-        // if the line contains '=' after the invalid sequence, possibly the
-        // error is in the key (like, invalid character in bare key).
-        const auto line_end = std::find(loc.iter(), loc.end(), '\n');
-        if(std::find(loc.iter(), line_end, '=') != line_end)
-        {
-            msg = format_underline("toml::parse_key_value_pair: "
-                "invalid format for key",
-                {{source_location(loc), "invalid character in key"}},
-                {"Did you forget '.' to separate dotted-key?",
-                "Allowed characters for bare key are [0-9a-zA-Z_-]."});
-        }
-        else // if not, the error is lack of key-value separator.
-        {
-            msg = format_underline("toml::parse_key_value_pair: "
-                "missing key-value separator `=`",
-                {{source_location(loc), "should be `=`"}});
-        }
-        loc.reset(first);
-        return err(std::move(msg));
-    }
-
-    const auto after_kvsp = loc.iter(); // err msg
-    auto val = parse_value<value_type>(loc);
-    if(!val)
-    {
-        std::string msg;
-        loc.reset(after_kvsp);
-        // check there is something not a comment/whitespace after `=`
-        if(sequence<maybe<lex_ws>, maybe<lex_comment>, lex_newline>::invoke(loc))
-        {
-            loc.reset(after_kvsp);
-            msg = format_underline("toml::parse_key_value_pair: "
-                    "missing value after key-value separator '='",
-                    {{source_location(loc), "expected value, but got nothing"}});
-        }
-        else // there is something not a comment/whitespace, so invalid format.
-        {
-            msg = std::move(val.unwrap_err());
-        }
-        loc.reset(first);
-        return err(msg);
-    }
-    return ok(std::make_pair(std::move(key_reg.unwrap()),
-                             std::move(val.unwrap())));
-}
-
-// for error messages.
-template<typename InputIterator>
-std::string format_dotted_keys(InputIterator first, const InputIterator last)
-{
-    static_assert(std::is_same<key,
-        typename std::iterator_traits<InputIterator>::value_type>::value,"");
-
-    std::string retval(*first++);
-    for(; first != last; ++first)
-    {
-        retval += '.';
-        retval += *first;
-    }
-    return retval;
-}
-
-// forward decl for is_valid_forward_table_definition
-result<std::pair<std::vector<key>, region>, std::string>
-parse_table_key(location& loc);
-template<typename Value>
-result<std::pair<typename Value::table_type, region>, std::string>
-parse_inline_table(location& loc);
-
-// The following toml file is allowed.
-// ```toml
-// [a.b.c]     # here, table `a` has element `b`.
-// foo = "bar"
-// [a]         # merge a = {baz = "qux"} to a = {b = {...}}
-// baz = "qux"
-// ```
-// But the following is not allowed.
-// ```toml
-// [a]
-// b.c.foo = "bar"
-// [a]             # error! the same table [a] defined!
-// baz = "qux"
-// ```
-// The following is neither allowed.
-// ```toml
-// a = { b.c.foo = "bar"}
-// [a]             # error! the same table [a] defined!
-// baz = "qux"
-// ```
-// Here, it parses region of `tab->at(k)` as a table key and check the depth
-// of the key. If the key region points deeper node, it would be allowed.
-// Otherwise, the key points the same node. It would be rejected.
-template<typename Value, typename Iterator>
-bool is_valid_forward_table_definition(const Value& fwd, const Value& inserting,
-        Iterator key_first, Iterator key_curr, Iterator key_last)
-{
-    // ------------------------------------------------------------------------
-    // check type of the value to be inserted/merged
-
-    std::string inserting_reg = "";
-    if(const auto ptr = detail::get_region(inserting))
-    {
-        inserting_reg = ptr->str();
-    }
-    location inserting_def("internal", std::move(inserting_reg));
-    if(const auto inlinetable = parse_inline_table<Value>(inserting_def))
-    {
-        // check if we are overwriting existing table.
-        // ```toml
-        // # NG
-        // a.b = 42
-        // a = {d = 3.14}
-        // ```
-        // Inserting an inline table to a existing super-table is not allowed in
-        // any case. If we found it, we can reject it without further checking.
-        return false;
-    }
-
-    // ------------------------------------------------------------------------
-    // check table defined before
-
-    std::string internal = "";
-    if(const auto ptr = detail::get_region(fwd))
-    {
-        internal = ptr->str();
-    }
-    location def("internal", std::move(internal));
-    if(const auto tabkeys = parse_table_key(def)) // [table.key]
-    {
-        // table keys always contains all the nodes from the root.
-        const auto& tks = tabkeys.unwrap().first;
-        if(std::size_t(std::distance(key_first, key_last)) == tks.size() &&
-           std::equal(tks.begin(), tks.end(), key_first))
-        {
-            // the keys are equivalent. it is not allowed.
-            return false;
-        }
-        // the keys are not equivalent. it is allowed.
-        return true;
-    }
-    if(const auto dotkeys = parse_key(def))
-    {
-        // consider the following case.
-        // [a]
-        // b.c = {d = 42}
-        // [a.b.c]
-        // e = 2.71
-        // this defines the table [a.b.c] twice. no?
-
-        // a dotted key starts from the node representing a table in which the
-        // dotted key belongs to.
-        const auto& dks = dotkeys.unwrap().first;
-        if(std::size_t(std::distance(key_curr, key_last)) == dks.size() &&
-           std::equal(dks.begin(), dks.end(), key_curr))
-        {
-            // the keys are equivalent. it is not allowed.
-            return false;
-        }
-        // the keys are not equivalent. it is allowed.
-        return true;
-    }
-    return false;
-}
-
-template<typename Value, typename InputIterator>
-result<bool, std::string>
-insert_nested_key(typename Value::table_type& root, const Value& v,
-                  InputIterator iter, const InputIterator last,
-                  region key_reg,
-                  const bool is_array_of_table = false)
-{
-    static_assert(std::is_same<key,
-        typename std::iterator_traits<InputIterator>::value_type>::value,"");
-
-    using value_type = Value;
-    using table_type = typename value_type::table_type;
-    using array_type = typename value_type::array_type;
-
-    const auto first = iter;
-    assert(iter != last);
-
-    table_type* tab = std::addressof(root);
-    for(; iter != last; ++iter) // search recursively
-    {
-        const key& k = *iter;
-        if(std::next(iter) == last) // k is the last key
-        {
-            // XXX if the value is array-of-tables, there can be several
-            //     tables that are in the same array. in that case, we need to
-            //     find the last element and insert it to there.
-            if(is_array_of_table)
-            {
-                if(tab->count(k) == 1) // there is already an array of table
-                {
-                    if(tab->at(k).is_table())
-                    {
-                        // show special err msg for conflicting table
-                        throw syntax_error(format_underline(concat_to_string(
-                            "toml::insert_value: array of table (\"",
-                            format_dotted_keys(first, last),
-                            "\") cannot be defined"), {
-                                {tab->at(k).location(), "table already defined"},
-                                {v.location(), "this conflicts with the previous table"}
-                            }), v.location());
-                    }
-                    else if(!(tab->at(k).is_array()))
-                    {
-                        throw syntax_error(format_underline(concat_to_string(
-                            "toml::insert_value: array of table (\"",
-                            format_dotted_keys(first, last), "\") collides with"
-                            " existing value"), {
-                                {tab->at(k).location(),
-                                 concat_to_string("this ", tab->at(k).type(),
-                                                  " value already exists")},
-                                {v.location(),
-                                 "while inserting this array-of-tables"}
-                            }), v.location());
-                    }
-                    // the above if-else-if checks tab->at(k) is an array
-                    auto& a = tab->at(k).as_array();
-                    // If table element is defined as [[array_of_tables]], it
-                    // cannot be an empty array. If an array of tables is
-                    // defined as `aot = []`, it cannot be appended.
-                    if(a.empty() || !(a.front().is_table()))
-                    {
-                        throw syntax_error(format_underline(concat_to_string(
-                            "toml::insert_value: array of table (\"",
-                            format_dotted_keys(first, last), "\") collides with"
-                            " existing value"), {
-                                {tab->at(k).location(),
-                                 concat_to_string("this ", tab->at(k).type(),
-                                                  " value already exists")},
-                                {v.location(),
-                                 "while inserting this array-of-tables"}
-                            }), v.location());
-                    }
-                    // avoid conflicting array of table like the following.
-                    // ```toml
-                    // a = [{b = 42}] # define a as an array of *inline* tables
-                    // [[a]]          # a is an array of *multi-line* tables
-                    // b = 54
-                    // ```
-                    // Here, from the type information, these cannot be detected
-                    // because inline table is also a table.
-                    // But toml v0.5.0 explicitly says it is invalid. The above
-                    // array-of-tables has a static size and appending to the
-                    // array is invalid.
-                    // In this library, multi-line table value has a region
-                    // that points to the key of the table (e.g. [[a]]). By
-                    // comparing the first two letters in key, we can detect
-                    // the array-of-table is inline or multiline.
-                    if(const auto ptr = detail::get_region(a.front()))
-                    {
-                        if(ptr->str().substr(0,2) != "[[")
-                        {
-                            throw syntax_error(format_underline(concat_to_string(
-                                "toml::insert_value: array of table (\"",
-                                format_dotted_keys(first, last), "\") collides "
-                                "with existing array-of-tables"), {
-                                    {tab->at(k).location(),
-                                     concat_to_string("this ", tab->at(k).type(),
-                                                      " value has static size")},
-                                    {v.location(),
-                                     "appending it to the statically sized array"}
-                                }), v.location());
-                        }
-                    }
-                    a.push_back(v);
-                    return ok(true);
-                }
-                else // if not, we need to create the array of table
-                {
-                    // XXX: Consider the following array of tables.
-                    // ```toml
-                    // # This is a comment.
-                    // [[aot]]
-                    // foo = "bar"
-                    // ```
-                    // Here, the comment is for `aot`. But here, actually two
-                    // values are defined. An array that contains tables, named
-                    // `aot`, and the 0th element of the `aot`, `{foo = "bar"}`.
-                    // Those two are different from each other. But both of them
-                    // points to the same portion of the TOML file, `[[aot]]`,
-                    // so `key_reg.comments()` returns `# This is a comment`.
-                    // If it is assigned as a comment of `aot` defined here, the
-                    // comment will be duplicated. Both the `aot` itself and
-                    // the 0-th element will have the same comment. This causes
-                    // "duplication of the same comments" bug when the data is
-                    // serialized.
-                    //     Next, consider the following.
-                    // ```toml
-                    // # comment 1
-                    // aot = [
-                    //     # comment 2
-                    //     {foo = "bar"},
-                    // ]
-                    // ```
-                    // In this case, we can distinguish those two comments. So
-                    // here we need to add "comment 1" to the `aot` and
-                    // "comment 2" to the 0th element of that.
-                    //     To distinguish those two, we check the key region.
-                    std::vector<std::string> comments{/* empty by default */};
-                    if(key_reg.str().substr(0, 2) != "[[")
-                    {
-                        comments = key_reg.comments();
-                    }
-                    value_type aot(array_type(1, v), key_reg, std::move(comments));
-                    tab->insert(std::make_pair(k, aot));
-                    return ok(true);
-                }
-            } // end if(array of table)
-
-            if(tab->count(k) == 1)
-            {
-                if(tab->at(k).is_table() && v.is_table())
-                {
-                    if(!is_valid_forward_table_definition(
-                                tab->at(k), v, first, iter, last))
-                    {
-                        throw syntax_error(format_underline(concat_to_string(
-                            "toml::insert_value: table (\"",
-                            format_dotted_keys(first, last),
-                            "\") already exists."), {
-                                {tab->at(k).location(), "table already exists here"},
-                                {v.location(), "table defined twice"}
-                            }), v.location());
-                    }
-                    // to allow the following toml file.
-                    // [a.b.c]
-                    // d = 42
-                    // [a]
-                    // e = 2.71
-                    auto& t = tab->at(k).as_table();
-                    for(const auto& kv : v.as_table())
-                    {
-                        if(tab->at(k).contains(kv.first))
-                        {
-                            throw syntax_error(format_underline(concat_to_string(
-                                "toml::insert_value: value (\"",
-                                format_dotted_keys(first, last),
-                                "\") already exists."), {
-                                    {t.at(kv.first).location(), "already exists here"},
-                                    {v.location(), "this defined twice"}
-                                }), v.location());
-                        }
-                        t[kv.first] = kv.second;
-                    }
-                    detail::change_region(tab->at(k), key_reg);
-                    return ok(true);
-                }
-                else if(v.is_table()                     &&
-                        tab->at(k).is_array()            &&
-                        tab->at(k).as_array().size() > 0 &&
-                        tab->at(k).as_array().front().is_table())
-                {
-                    throw syntax_error(format_underline(concat_to_string(
-                        "toml::insert_value: array of tables (\"",
-                        format_dotted_keys(first, last), "\") already exists."), {
-                            {tab->at(k).location(), "array of tables defined here"},
-                            {v.location(), "table conflicts with the previous array of table"}
-                        }), v.location());
-                }
-                else
-                {
-                    throw syntax_error(format_underline(concat_to_string(
-                        "toml::insert_value: value (\"",
-                        format_dotted_keys(first, last), "\") already exists."), {
-                            {tab->at(k).location(), "value already exists here"},
-                            {v.location(), "value defined twice"}
-                        }), v.location());
-                }
-            }
-            tab->insert(std::make_pair(k, v));
-            return ok(true);
-        }
-        else // k is not the last one, we should insert recursively
-        {
-            // if there is no corresponding value, insert it first.
-            // related: you don't need to write
-            // # [x]
-            // # [x.y]
-            // to write
-            // [x.y.z]
-            if(tab->count(k) == 0)
-            {
-                // a table that is defined implicitly doesn't have any comments.
-                (*tab)[k] = value_type(table_type{}, key_reg, {/*no comment*/});
-            }
-
-            // type checking...
-            if(tab->at(k).is_table())
-            {
-                // According to toml-lang/toml:36d3091b3 "Clarify that inline
-                // tables are immutable", check if it adds key-value pair to an
-                // inline table.
-                if(const auto* ptr = get_region(tab->at(k)))
-                {
-                    // here, if the value is a (multi-line) table, the region
-                    // should be something like `[table-name]`.
-                    if(ptr->front() == '{')
-                    {
-                        throw syntax_error(format_underline(concat_to_string(
-                            "toml::insert_value: inserting to an inline table (",
-                            format_dotted_keys(first, std::next(iter)),
-                            ") but inline tables are immutable"), {
-                                {tab->at(k).location(), "inline tables are immutable"},
-                                {v.location(), "inserting this"}
-                            }), v.location());
-                    }
-                }
-                tab = std::addressof((*tab)[k].as_table());
-            }
-            else if(tab->at(k).is_array()) // inserting to array-of-tables?
-            {
-                auto& a = (*tab)[k].as_array();
-                if(!a.back().is_table())
-                {
-                    throw syntax_error(format_underline(concat_to_string(
-                        "toml::insert_value: target (",
-                        format_dotted_keys(first, std::next(iter)),
-                        ") is neither table nor an array of tables"), {
-                            {a.back().location(), concat_to_string(
-                                    "actual type is ", a.back().type())},
-                            {v.location(), "inserting this"}
-                        }), v.location());
-                }
-                tab = std::addressof(a.back().as_table());
-            }
-            else
-            {
-                throw syntax_error(format_underline(concat_to_string(
-                    "toml::insert_value: target (",
-                    format_dotted_keys(first, std::next(iter)),
-                    ") is neither table nor an array of tables"), {
-                        {tab->at(k).location(), concat_to_string(
-                                "actual type is ", tab->at(k).type())},
-                        {v.location(), "inserting this"}
-                    }), v.location());
-            }
-        }
-    }
-    return err(std::string("toml::detail::insert_nested_key: never reach here"));
-}
-
-template<typename Value>
-result<std::pair<typename Value::table_type, region>, std::string>
-parse_inline_table(location& loc)
-{
-    using value_type = Value;
-    using table_type = typename value_type::table_type;
-
-    const auto first = loc.iter();
-    table_type retval;
-    if(!(loc.iter() != loc.end() && *loc.iter() == '{'))
-    {
-        return err(format_underline("toml::parse_inline_table: ",
-            {{source_location(loc), "the next token is not an inline table"}}));
-    }
-    loc.advance();
-
-    // check if the inline table is an empty table = { }
-    maybe<lex_ws>::invoke(loc);
-    if(loc.iter() != loc.end() && *loc.iter() == '}')
-    {
-        loc.advance(); // skip `}`
-        return ok(std::make_pair(retval, region(loc, first, loc.iter())));
-    }
-
-    // it starts from "{". it should be formatted as inline-table
-    while(loc.iter() != loc.end())
-    {
-        const auto kv_r = parse_key_value_pair<value_type>(loc);
-        if(!kv_r)
-        {
-            return err(kv_r.unwrap_err());
-        }
-
-        const auto&              kvpair  = kv_r.unwrap();
-        const std::vector<key>&  keys    = kvpair.first.first;
-        const auto&              key_reg = kvpair.first.second;
-        const value_type&        val     = kvpair.second;
-
-        const auto inserted =
-            insert_nested_key(retval, val, keys.begin(), keys.end(), key_reg);
-        if(!inserted)
-        {
-            throw internal_error("toml::parse_inline_table: "
-                "failed to insert value into table: " + inserted.unwrap_err(),
-                source_location(loc));
-        }
-
-        using lex_table_separator = sequence<maybe<lex_ws>, character<','>>;
-        const auto sp = lex_table_separator::invoke(loc);
-
-        if(!sp)
-        {
-            maybe<lex_ws>::invoke(loc);
-
-            if(loc.iter() == loc.end())
-            {
-                throw syntax_error(format_underline(
-                    "toml::parse_inline_table: missing table separator `}` ",
-                    {{source_location(loc), "should be `}`"}}),
-                    source_location(loc));
-            }
-            else if(*loc.iter() == '}')
-            {
-                loc.advance(); // skip `}`
-                return ok(std::make_pair(
-                            retval, region(loc, first, loc.iter())));
-            }
-            else if(*loc.iter() == '#' || *loc.iter() == '\r' || *loc.iter() == '\n')
-            {
-                throw syntax_error(format_underline(
-                    "toml::parse_inline_table: missing curly brace `}`",
-                    {{source_location(loc), "should be `}`"}}),
-                    source_location(loc));
-            }
-            else
-            {
-                throw syntax_error(format_underline(
-                    "toml::parse_inline_table: missing table separator `,` ",
-                    {{source_location(loc), "should be `,`"}}),
-                    source_location(loc));
-            }
-        }
-        else // `,` is found
-        {
-            maybe<lex_ws>::invoke(loc);
-            if(loc.iter() != loc.end() && *loc.iter() == '}')
-            {
-                throw syntax_error(format_underline(
-                    "toml::parse_inline_table: trailing comma is not allowed in"
-                    " an inline table",
-                    {{source_location(loc), "should be `}`"}}),
-                    source_location(loc));
-            }
-        }
-    }
-    loc.reset(first);
-    throw syntax_error(format_underline("toml::parse_inline_table: "
-            "inline table did not closed by `}`",
-            {{source_location(loc), "should be closed"}}),
-            source_location(loc));
-}
-
-inline result<value_t, std::string> guess_number_type(const location& l)
-{
-    // This function tries to find some (common) mistakes by checking characters
-    // that follows the last character of a value. But it is often difficult
-    // because some non-newline characters can appear after a value. E.g.
-    // spaces, tabs, commas (in an array or inline table), closing brackets
-    // (of an array or inline table), comment-sign (#). Since this function
-    // does not parse further, those characters are always allowed to be there.
-    location loc = l;
-
-    if(lex_offset_date_time::invoke(loc)) {return ok(value_t::offset_datetime);}
-    loc.reset(l.iter());
-
-    if(lex_local_date_time::invoke(loc))
-    {
-        // bad offset may appear after this.
-        if(loc.iter() != loc.end() && (*loc.iter() == '+' || *loc.iter() == '-'
-                    || *loc.iter() == 'Z' || *loc.iter() == 'z'))
-        {
-            return err(format_underline("bad offset: should be [+-]HH:MM or Z",
-                        {{source_location(loc), "[+-]HH:MM or Z"}},
-                        {"pass: +09:00, -05:30", "fail: +9:00, -5:30"}));
-        }
-        return ok(value_t::local_datetime);
-    }
-    loc.reset(l.iter());
-
-    if(lex_local_date::invoke(loc))
-    {
-        // bad time may appear after this.
-        // A space is allowed as a delimiter between local time. But there are
-        // both cases in which a space becomes valid or invalid.
-        // - invalid: 2019-06-16 7:00:00
-        // - valid  : 2019-06-16 07:00:00
-        if(loc.iter() != loc.end())
-        {
-            const auto c = *loc.iter();
-            if(c == 'T' || c == 't')
-            {
-                return err(format_underline("bad time: should be HH:MM:SS.subsec",
-                        {{source_location(loc), "HH:MM:SS.subsec"}},
-                        {"pass: 1979-05-27T07:32:00, 1979-05-27 07:32:00.999999",
-                         "fail: 1979-05-27T7:32:00, 1979-05-27 17:32"}));
-            }
-            if('0' <= c && c <= '9')
-            {
-                return err(format_underline("bad time: missing T",
-                        {{source_location(loc), "T or space required here"}},
-                        {"pass: 1979-05-27T07:32:00, 1979-05-27 07:32:00.999999",
-                         "fail: 1979-05-27T7:32:00, 1979-05-27 7:32"}));
-            }
-            if(c == ' ' && std::next(loc.iter()) != loc.end() &&
-                ('0' <= *std::next(loc.iter()) && *std::next(loc.iter())<= '9'))
-            {
-                loc.advance();
-                return err(format_underline("bad time: should be HH:MM:SS.subsec",
-                        {{source_location(loc), "HH:MM:SS.subsec"}},
-                        {"pass: 1979-05-27T07:32:00, 1979-05-27 07:32:00.999999",
-                         "fail: 1979-05-27T7:32:00, 1979-05-27 7:32"}));
-            }
-        }
-        return ok(value_t::local_date);
-    }
-    loc.reset(l.iter());
-
-    if(lex_local_time::invoke(loc)) {return ok(value_t::local_time);}
-    loc.reset(l.iter());
-
-    if(lex_float::invoke(loc))
-    {
-        if(loc.iter() != loc.end() && *loc.iter() == '_')
-        {
-            return err(format_underline("bad float: `_` should be surrounded by digits",
-                        {{source_location(loc), "here"}},
-                        {"pass: +1.0, -2e-2, 3.141_592_653_589, inf, nan",
-                         "fail: .0, 1., _1.0, 1.0_, 1_.0, 1.0__0"}));
-        }
-        return ok(value_t::floating);
-    }
-    loc.reset(l.iter());
-
-    if(lex_integer::invoke(loc))
-    {
-        if(loc.iter() != loc.end())
-        {
-            const auto c = *loc.iter();
-            if(c == '_')
-            {
-                return err(format_underline("bad integer: `_` should be surrounded by digits",
-                            {{source_location(loc), "here"}},
-                            {"pass: -42, 1_000, 1_2_3_4_5, 0xC0FFEE, 0b0010, 0o755",
-                             "fail: 1__000, 0123"}));
-            }
-            if('0' <= c && c <= '9')
-            {
-                // leading zero. point '0'
-                loc.retrace();
-                return err(format_underline("bad integer: leading zero",
-                            {{source_location(loc), "here"}},
-                            {"pass: -42, 1_000, 1_2_3_4_5, 0xC0FFEE, 0b0010, 0o755",
-                             "fail: 1__000, 0123"}));
-            }
-            if(c == ':' || c == '-')
-            {
-                return err(format_underline("bad datetime: invalid format",
-                            {{source_location(loc), "here"}},
-                            {"pass: 1979-05-27T07:32:00-07:00, 1979-05-27 07:32:00.999999Z",
-                             "fail: 1979-05-27T7:32:00-7:00, 1979-05-27 7:32-00:30"}));
-            }
-            if(c == '.' || c == 'e' || c == 'E')
-            {
-                return err(format_underline("bad float: invalid format",
-                            {{source_location(loc), "here"}},
-                            {"pass: +1.0, -2e-2, 3.141_592_653_589, inf, nan",
-                             "fail: .0, 1., _1.0, 1.0_, 1_.0, 1.0__0"}));
-            }
-        }
-        return ok(value_t::integer);
-    }
-    if(loc.iter() != loc.end() && *loc.iter() == '.')
-    {
-        return err(format_underline("bad float: invalid format",
-                {{source_location(loc), "integer part required before this"}},
-                {"pass: +1.0, -2e-2, 3.141_592_653_589, inf, nan",
-                 "fail: .0, 1., _1.0, 1.0_, 1_.0, 1.0__0"}));
-    }
-    if(loc.iter() != loc.end() && *loc.iter() == '_')
-    {
-        return err(format_underline("bad number: `_` should be surrounded by digits",
-                {{source_location(loc), "`_` is not surrounded by digits"}},
-                {"pass: -42, 1_000, 1_2_3_4_5, 0xC0FFEE, 0b0010, 0o755",
-                 "fail: 1__000, 0123"}));
-    }
-    return err(format_underline("bad format: unknown value appeared",
-                {{source_location(loc), "here"}}));
-}
-
-inline result<value_t, std::string> guess_value_type(const location& loc)
-{
-    switch(*loc.iter())
-    {
-        case '"' : {return ok(value_t::string);  }
-        case '\'': {return ok(value_t::string);  }
-        case 't' : {return ok(value_t::boolean); }
-        case 'f' : {return ok(value_t::boolean); }
-        case '[' : {return ok(value_t::array);   }
-        case '{' : {return ok(value_t::table);   }
-        case 'i' : {return ok(value_t::floating);} // inf.
-        case 'n' : {return ok(value_t::floating);} // nan.
-        default  : {return guess_number_type(loc);}
-    }
-}
-
-template<typename Value, typename T>
-result<Value, std::string>
-parse_value_helper(result<std::pair<T, region>, std::string> rslt)
-{
-    if(rslt.is_ok())
-    {
-        auto comments = rslt.as_ok().second.comments();
-        return ok(Value(std::move(rslt.as_ok()), std::move(comments)));
-    }
-    else
-    {
-        return err(std::move(rslt.as_err()));
-    }
-}
-
-template<typename Value>
-result<Value, std::string> parse_value(location& loc)
-{
-    const auto first = loc.iter();
-    if(first == loc.end())
-    {
-        return err(format_underline("toml::parse_value: input is empty",
-                   {{source_location(loc), ""}}));
-    }
-
-    const auto type = guess_value_type(loc);
-    if(!type)
-    {
-        return err(type.unwrap_err());
-    }
-
-    switch(type.unwrap())
-    {
-        case value_t::boolean        : {return parse_value_helper<Value>(parse_boolean(loc)            );}
-        case value_t::integer        : {return parse_value_helper<Value>(parse_integer(loc)            );}
-        case value_t::floating       : {return parse_value_helper<Value>(parse_floating(loc)           );}
-        case value_t::string         : {return parse_value_helper<Value>(parse_string(loc)             );}
-        case value_t::offset_datetime: {return parse_value_helper<Value>(parse_offset_datetime(loc)    );}
-        case value_t::local_datetime : {return parse_value_helper<Value>(parse_local_datetime(loc)     );}
-        case value_t::local_date     : {return parse_value_helper<Value>(parse_local_date(loc)         );}
-        case value_t::local_time     : {return parse_value_helper<Value>(parse_local_time(loc)         );}
-        case value_t::array          : {return parse_value_helper<Value>(parse_array<Value>(loc)       );}
-        case value_t::table          : {return parse_value_helper<Value>(parse_inline_table<Value>(loc));}
-        default:
-        {
-            const auto msg = format_underline("toml::parse_value: "
-                    "unknown token appeared", {{source_location(loc), "unknown"}});
-            loc.reset(first);
-            return err(msg);
-        }
-    }
-}
-
-inline result<std::pair<std::vector<key>, region>, std::string>
-parse_table_key(location& loc)
-{
-    if(auto token = lex_std_table::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto open = lex_std_table_open::invoke(inner_loc);
-        if(!open || inner_loc.iter() == inner_loc.end())
-        {
-            throw internal_error(format_underline(
-                "toml::parse_table_key: no `[`",
-                {{source_location(inner_loc), "should be `[`"}}),
-                source_location(inner_loc));
-        }
-        // to skip [ a . b . c ]
-        //          ^----------- this whitespace
-        lex_ws::invoke(inner_loc);
-        const auto keys = parse_key(inner_loc);
-        if(!keys)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_table_key: invalid key",
-                {{source_location(inner_loc), "not key"}}),
-                source_location(inner_loc));
-        }
-        // to skip [ a . b . c ]
-        //                    ^-- this whitespace
-        lex_ws::invoke(inner_loc);
-        const auto close = lex_std_table_close::invoke(inner_loc);
-        if(!close)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_table_key: no `]`",
-                {{source_location(inner_loc), "should be `]`"}}),
-                source_location(inner_loc));
-        }
-
-        // after [table.key], newline or EOF(empty table) required.
-        if(loc.iter() != loc.end())
-        {
-            using lex_newline_after_table_key =
-                sequence<maybe<lex_ws>, maybe<lex_comment>, lex_newline>;
-            const auto nl = lex_newline_after_table_key::invoke(loc);
-            if(!nl)
-            {
-                throw syntax_error(format_underline(
-                    "toml::parse_table_key: newline required after [table.key]",
-                    {{source_location(loc), "expected newline"}}),
-                    source_location(loc));
-            }
-        }
-        return ok(std::make_pair(keys.unwrap().first, token.unwrap()));
-    }
-    else
-    {
-        return err(format_underline("toml::parse_table_key: "
-            "not a valid table key", {{source_location(loc), "here"}}));
-    }
-}
-
-inline result<std::pair<std::vector<key>, region>, std::string>
-parse_array_table_key(location& loc)
-{
-    if(auto token = lex_array_table::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-
-        const auto open = lex_array_table_open::invoke(inner_loc);
-        if(!open || inner_loc.iter() == inner_loc.end())
-        {
-            throw internal_error(format_underline(
-                "toml::parse_array_table_key: no `[[`",
-                {{source_location(inner_loc), "should be `[[`"}}),
-                source_location(inner_loc));
-        }
-        lex_ws::invoke(inner_loc);
-        const auto keys = parse_key(inner_loc);
-        if(!keys)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_array_table_key: invalid key",
-                {{source_location(inner_loc), "not a key"}}),
-                source_location(inner_loc));
-        }
-        lex_ws::invoke(inner_loc);
-        const auto close = lex_array_table_close::invoke(inner_loc);
-        if(!close)
-        {
-            throw internal_error(format_underline(
-                "toml::parse_table_key: no `]]`",
-                {{source_location(inner_loc), "should be `]]`"}}),
-                source_location(inner_loc));
-        }
-
-        // after [[table.key]], newline or EOF(empty table) required.
-        if(loc.iter() != loc.end())
-        {
-            using lex_newline_after_table_key =
-                sequence<maybe<lex_ws>, maybe<lex_comment>, lex_newline>;
-            const auto nl = lex_newline_after_table_key::invoke(loc);
-            if(!nl)
-            {
-                throw syntax_error(format_underline("toml::"
-                    "parse_array_table_key: newline required after [[table.key]]",
-                    {{source_location(loc), "expected newline"}}),
-                    source_location(loc));
-            }
-        }
-        return ok(std::make_pair(keys.unwrap().first, token.unwrap()));
-    }
-    else
-    {
-        return err(format_underline("toml::parse_array_table_key: "
-            "not a valid table key", {{source_location(loc), "here"}}));
-    }
-}
-
-// parse table body (key-value pairs until the iter hits the next [tablekey])
-template<typename Value>
-result<typename Value::table_type, std::string>
-parse_ml_table(location& loc)
-{
-    using value_type = Value;
-    using table_type = typename value_type::table_type;
-
-    const auto first = loc.iter();
-    if(first == loc.end())
-    {
-        return ok(table_type{});
-    }
-
-    // XXX at lest one newline is needed.
-    using skip_line = repeat<
-        sequence<maybe<lex_ws>, maybe<lex_comment>, lex_newline>, at_least<1>>;
-    skip_line::invoke(loc);
-    lex_ws::invoke(loc);
-
-    table_type tab;
-    while(loc.iter() != loc.end())
-    {
-        lex_ws::invoke(loc);
-        const auto before = loc.iter();
-        if(const auto tmp = parse_array_table_key(loc)) // next table found
-        {
-            loc.reset(before);
-            return ok(tab);
-        }
-        if(const auto tmp = parse_table_key(loc)) // next table found
-        {
-            loc.reset(before);
-            return ok(tab);
-        }
-
-        if(const auto kv = parse_key_value_pair<value_type>(loc))
-        {
-            const auto&              kvpair  = kv.unwrap();
-            const std::vector<key>&  keys    = kvpair.first.first;
-            const auto&              key_reg = kvpair.first.second;
-            const value_type&        val     = kvpair.second;
-            const auto inserted =
-                insert_nested_key(tab, val, keys.begin(), keys.end(), key_reg);
-            if(!inserted)
-            {
-                return err(inserted.unwrap_err());
-            }
-        }
-        else
-        {
-            return err(kv.unwrap_err());
-        }
-
-        // comment lines are skipped by the above function call.
-        // However, since the `skip_line` requires at least 1 newline, it fails
-        // if the file ends with ws and/or comment without newline.
-        // `skip_line` matches `ws? + comment? + newline`, not `ws` or `comment`
-        // itself. To skip the last ws and/or comment, call lexers.
-        // It does not matter if these fails, so the return value is discarded.
-        lex_ws::invoke(loc);
-        lex_comment::invoke(loc);
-
-        // skip_line is (whitespace? comment? newline)_{1,}. multiple empty lines
-        // and comments after the last key-value pairs are allowed.
-        const auto newline = skip_line::invoke(loc);
-        if(!newline && loc.iter() != loc.end())
-        {
-            const auto before2 = loc.iter();
-            lex_ws::invoke(loc); // skip whitespace
-            const auto msg = format_underline("toml::parse_table: "
-                "invalid line format", {{source_location(loc), concat_to_string(
-                "expected newline, but got '", show_char(*loc.iter()), "'.")}});
-            loc.reset(before2);
-            return err(msg);
-        }
-
-        // the skip_lines only matches with lines that includes newline.
-        // to skip the last line that includes comment and/or whitespace
-        // but no newline, call them one more time.
-        lex_ws::invoke(loc);
-        lex_comment::invoke(loc);
-    }
-    return ok(tab);
-}
-
-template<typename Value>
-result<Value, std::string> parse_toml_file(location& loc)
-{
-    using value_type = Value;
-    using table_type = typename value_type::table_type;
-
-    const auto first = loc.iter();
-    if(first == loc.end())
-    {
-        // For empty files, return an empty table with an empty region (zero-length).
-        // Without the region, error messages would miss the filename.
-        return ok(value_type(table_type{}, region(loc, first, first), {}));
-    }
-
-    // put the first line as a region of a file
-    // Here first != loc.end(), so taking std::next is okay
-    const region file(loc, first, std::next(loc.iter()));
-
-    // The first successive comments that are separated from the first value
-    // by an empty line are for a file itself.
-    // ```toml
-    // # this is a comment for a file.
-    //
-    // key = "the first value"
-    // ```
-    // ```toml
-    // # this is a comment for "the first value".
-    // key = "the first value"
-    // ```
-    std::vector<std::string> comments;
-    using lex_first_comments = sequence<
-        repeat<sequence<maybe<lex_ws>, lex_comment, lex_newline>, at_least<1>>,
-        sequence<maybe<lex_ws>, lex_newline>
-        >;
-    if(const auto token = lex_first_comments::invoke(loc))
-    {
-        location inner_loc(loc.name(), token.unwrap().str());
-        while(inner_loc.iter() != inner_loc.end())
-        {
-            maybe<lex_ws>::invoke(inner_loc); // remove ws if exists
-            if(lex_newline::invoke(inner_loc))
-            {
-                assert(inner_loc.iter() == inner_loc.end());
-                break; // empty line found.
-            }
-            auto com = lex_comment::invoke(inner_loc).unwrap().str();
-            com.erase(com.begin()); // remove # sign
-            comments.push_back(std::move(com));
-            lex_newline::invoke(inner_loc);
-        }
-    }
-
-    table_type data;
-    // root object is also a table, but without [tablename]
-    if(const auto tab = parse_ml_table<value_type>(loc))
-    {
-        data = std::move(tab.unwrap());
-    }
-    else // failed (empty table is regarded as success in parse_ml_table)
-    {
-        return err(tab.unwrap_err());
-    }
-    while(loc.iter() != loc.end())
-    {
-        // here, the region of [table] is regarded as the table-key because
-        // the table body is normally too big and it is not so informative
-        // if the first key-value pair of the table is shown in the error
-        // message.
-        if(const auto tabkey = parse_array_table_key(loc))
-        {
-            const auto tab = parse_ml_table<value_type>(loc);
-            if(!tab){return err(tab.unwrap_err());}
-
-            const auto& tk   = tabkey.unwrap();
-            const auto& keys = tk.first;
-            const auto& reg  = tk.second;
-
-            const auto inserted = insert_nested_key(data,
-                    value_type(tab.unwrap(), reg, reg.comments()),
-                    keys.begin(), keys.end(), reg,
-                    /*is_array_of_table=*/ true);
-            if(!inserted) {return err(inserted.unwrap_err());}
-
-            continue;
-        }
-        if(const auto tabkey = parse_table_key(loc))
-        {
-            const auto tab = parse_ml_table<value_type>(loc);
-            if(!tab){return err(tab.unwrap_err());}
-
-            const auto& tk   = tabkey.unwrap();
-            const auto& keys = tk.first;
-            const auto& reg  = tk.second;
-
-            const auto inserted = insert_nested_key(data,
-                value_type(tab.unwrap(), reg, reg.comments()),
-                keys.begin(), keys.end(), reg);
-            if(!inserted) {return err(inserted.unwrap_err());}
-
-            continue;
-        }
-        return err(format_underline("toml::parse_toml_file: "
-            "unknown line appeared", {{source_location(loc), "unknown format"}}));
-    }
-
-    return ok(Value(std::move(data), file, comments));
-}
-
-} // detail
-
-template<typename                     Comment = TOML11_DEFAULT_COMMENT_STRATEGY,
-         template<typename ...> class Table   = std::unordered_map,
-         template<typename ...> class Array   = std::vector>
-basic_value<Comment, Table, Array>
-parse(std::istream& is, const std::string& fname = "unknown file")
-{
-    using value_type = basic_value<Comment, Table, Array>;
-
-    const auto beg = is.tellg();
-    is.seekg(0, std::ios::end);
-    const auto end = is.tellg();
-    const auto fsize = end - beg;
-    is.seekg(beg);
-
-    // read whole file as a sequence of char
-    assert(fsize >= 0);
-    std::vector<char> letters(static_cast<std::size_t>(fsize));
-    is.read(letters.data(), fsize);
-
-    // append LF.
-    // Although TOML does not require LF at the EOF, to make parsing logic
-    // simpler, we "normalize" the content by adding LF if it does not exist.
-    // It also checks if the last char is CR, to avoid changing the meaning.
-    // This is not the *best* way to deal with the last character, but is a
-    // simple and quick fix.
-    if(!letters.empty() && letters.back() != '\n' && letters.back() != '\r')
-    {
-        letters.push_back('\n');
-    }
-
-    detail::location loc(std::move(fname), std::move(letters));
-
-    // skip BOM if exists.
-    // XXX component of BOM (like 0xEF) exceeds the representable range of
-    // signed char, so on some (actually, most) of the environment, these cannot
-    // be compared to char. However, since we are always out of luck, we need to
-    // check our chars are equivalent to BOM. To do this, first we need to
-    // convert char to unsigned char to guarantee the comparability.
-    if(loc.source()->size() >= 3)
-    {
-        std::array<unsigned char, 3> BOM;
-        std::memcpy(BOM.data(), loc.source()->data(), 3);
-        if(BOM[0] == 0xEF && BOM[1] == 0xBB && BOM[2] == 0xBF)
-        {
-            loc.advance(3); // BOM found. skip.
-        }
-    }
-
-    const auto data = detail::parse_toml_file<value_type>(loc);
-    if(!data)
-    {
-        throw syntax_error(data.unwrap_err(), source_location(loc));
-    }
-    return data.unwrap();
-}
-
-template<typename                     Comment = TOML11_DEFAULT_COMMENT_STRATEGY,
-         template<typename ...> class Table   = std::unordered_map,
-         template<typename ...> class Array   = std::vector>
-basic_value<Comment, Table, Array> parse(const std::string& fname)
-{
-    std::ifstream ifs(fname.c_str(), std::ios_base::binary);
-    if(!ifs.good())
-    {
-        throw std::runtime_error("toml::parse: file open error -> " + fname);
-    }
-    return parse<Comment, Table, Array>(ifs, fname);
-}
-
-#ifdef TOML11_HAS_STD_FILESYSTEM
-// This function just forwards `parse("filename.toml")` to std::string version
-// to avoid the ambiguity in overload resolution.
-//
-// Both std::string and std::filesystem::path are convertible from const char*.
-// Without this, both parse(std::string) and parse(std::filesystem::path)
-// matches to parse("filename.toml"). This breaks the existing code.
-//
-// This function exactly matches to the invocation with c-string.
-// So this function is preferred than others and the ambiguity disappears.
-template<typename                     Comment = TOML11_DEFAULT_COMMENT_STRATEGY,
-         template<typename ...> class Table   = std::unordered_map,
-         template<typename ...> class Array   = std::vector>
-basic_value<Comment, Table, Array> parse(const char* fname)
-{
-    return parse<Comment, Table, Array>(std::string(fname));
-}
-
-template<typename                     Comment = TOML11_DEFAULT_COMMENT_STRATEGY,
-         template<typename ...> class Table   = std::unordered_map,
-         template<typename ...> class Array   = std::vector>
-basic_value<Comment, Table, Array> parse(const std::filesystem::path& fpath)
-{
-    std::ifstream ifs(fpath, std::ios_base::binary);
-    if(!ifs.good())
-    {
-        throw std::runtime_error("toml::parse: file open error -> " +
-                                 fpath.string());
-    }
-    return parse<Comment, Table, Array>(ifs, fpath.string());
-}
-#endif // TOML11_HAS_STD_FILESYSTEM
-
-} // toml
-#endif// TOML11_PARSER_HPP
diff --git a/src/toml11/toml/region.hpp b/src/toml11/toml/region.hpp
deleted file mode 100644
index 2e01e51d0..000000000
--- a/src/toml11/toml/region.hpp
+++ /dev/null
@@ -1,417 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_REGION_HPP
-#define TOML11_REGION_HPP
-#include <memory>
-#include <vector>
-#include <algorithm>
-#include <initializer_list>
-#include <iterator>
-#include <iomanip>
-#include <cassert>
-#include "color.hpp"
-
-namespace toml
-{
-namespace detail
-{
-
-// helper function to avoid std::string(0, 'c') or std::string(iter, iter)
-template<typename Iterator>
-std::string make_string(Iterator first, Iterator last)
-{
-    if(first == last) {return "";}
-    return std::string(first, last);
-}
-inline std::string make_string(std::size_t len, char c)
-{
-    if(len == 0) {return "";}
-    return std::string(len, c);
-}
-
-// region_base is a base class of location and region that are defined below.
-// it will be used to generate better error messages.
-struct region_base
-{
-    region_base() = default;
-    virtual ~region_base() = default;
-    region_base(const region_base&) = default;
-    region_base(region_base&&     ) = default;
-    region_base& operator=(const region_base&) = default;
-    region_base& operator=(region_base&&     ) = default;
-
-    virtual bool is_ok()           const noexcept {return false;}
-    virtual char front()           const noexcept {return '\0';}
-
-    virtual std::string str()      const {return std::string("unknown region");}
-    virtual std::string name()     const {return std::string("unknown file");}
-    virtual std::string line()     const {return std::string("unknown line");}
-    virtual std::string line_num() const {return std::string("?");}
-
-    // length of the region
-    virtual std::size_t size()     const noexcept {return 0;}
-    // number of characters in the line before the region
-    virtual std::size_t before()   const noexcept {return 0;}
-    // number of characters in the line after the region
-    virtual std::size_t after()    const noexcept {return 0;}
-
-    virtual std::vector<std::string> comments() const {return {};}
-    // ```toml
-    // # comment_before
-    // key = "value" # comment_inline
-    // ```
-};
-
-// location represents a position in a container, which contains a file content.
-// it can be considered as a region that contains only one character.
-//
-// it contains pointer to the file content and iterator that points the current
-// location.
-struct location final : public region_base
-{
-    using const_iterator  = typename std::vector<char>::const_iterator;
-    using difference_type = typename const_iterator::difference_type;
-    using source_ptr      = std::shared_ptr<const std::vector<char>>;
-
-    location(std::string source_name, std::vector<char> cont)
-      : source_(std::make_shared<std::vector<char>>(std::move(cont))),
-        line_number_(1), source_name_(std::move(source_name)), iter_(source_->cbegin())
-    {}
-    location(std::string source_name, const std::string& cont)
-      : source_(std::make_shared<std::vector<char>>(cont.begin(), cont.end())),
-        line_number_(1), source_name_(std::move(source_name)), iter_(source_->cbegin())
-    {}
-
-    location(const location&) = default;
-    location(location&&)      = default;
-    location& operator=(const location&) = default;
-    location& operator=(location&&)      = default;
-    ~location() = default;
-
-    bool is_ok() const noexcept override {return static_cast<bool>(source_);}
-    char front() const noexcept override {return *iter_;}
-
-    // this const prohibits codes like `++(loc.iter())`.
-    const const_iterator iter()  const noexcept {return iter_;}
-
-    const_iterator begin() const noexcept {return source_->cbegin();}
-    const_iterator end()   const noexcept {return source_->cend();}
-
-    // XXX `location::line_num()` used to be implemented using `std::count` to
-    // count a number of '\n'. But with a long toml file (typically, 10k lines),
-    // it becomes intolerably slow because each time it generates error messages,
-    // it counts '\n' from thousands of characters. To workaround it, I decided
-    // to introduce `location::line_number_` member variable and synchronize it
-    // to the location changes the point to look. So an overload of `iter()`
-    // which returns mutable reference is removed and `advance()`, `retrace()`
-    // and `reset()` is added.
-    void advance(difference_type n = 1) noexcept
-    {
-        this->line_number_ += static_cast<std::size_t>(
-                std::count(this->iter_, std::next(this->iter_, n), '\n'));
-        this->iter_ += n;
-        return;
-    }
-    void retrace(difference_type n = 1) noexcept
-    {
-        this->line_number_ -= static_cast<std::size_t>(
-                std::count(std::prev(this->iter_, n), this->iter_, '\n'));
-        this->iter_ -= n;
-        return;
-    }
-    void reset(const_iterator rollback) noexcept
-    {
-        // since c++11, std::distance works in both ways for random-access
-        // iterators and returns a negative value if `first > last`.
-        if(0 <= std::distance(rollback, this->iter_)) // rollback < iter
-        {
-            this->line_number_ -= static_cast<std::size_t>(
-                    std::count(rollback, this->iter_, '\n'));
-        }
-        else // iter < rollback [[unlikely]]
-        {
-            this->line_number_ += static_cast<std::size_t>(
-                    std::count(this->iter_, rollback, '\n'));
-        }
-        this->iter_ = rollback;
-        return;
-    }
-
-    std::string str()  const override {return make_string(1, *this->iter());}
-    std::string name() const override {return source_name_;}
-
-    std::string line_num() const override
-    {
-        return std::to_string(this->line_number_);
-    }
-
-    std::string line() const override
-    {
-        return make_string(this->line_begin(), this->line_end());
-    }
-
-    const_iterator line_begin() const noexcept
-    {
-        using reverse_iterator = std::reverse_iterator<const_iterator>;
-        return std::find(reverse_iterator(this->iter()),
-                         reverse_iterator(this->begin()), '\n').base();
-    }
-    const_iterator line_end() const noexcept
-    {
-        return std::find(this->iter(), this->end(), '\n');
-    }
-
-    // location is always points a character. so the size is 1.
-    std::size_t size() const noexcept override
-    {
-        return 1u;
-    }
-    std::size_t before() const noexcept override
-    {
-        const auto sz = std::distance(this->line_begin(), this->iter());
-        assert(sz >= 0);
-        return static_cast<std::size_t>(sz);
-    }
-    std::size_t after() const noexcept override
-    {
-        const auto sz = std::distance(this->iter(), this->line_end());
-        assert(sz >= 0);
-        return static_cast<std::size_t>(sz);
-    }
-
-    source_ptr const& source() const& noexcept {return source_;}
-    source_ptr&&      source() &&     noexcept {return std::move(source_);}
-
-  private:
-
-    source_ptr     source_;
-    std::size_t    line_number_;
-    std::string    source_name_;
-    const_iterator iter_;
-};
-
-// region represents a range in a container, which contains a file content.
-//
-// it contains pointer to the file content and iterator that points the first
-// and last location.
-struct region final : public region_base
-{
-    using const_iterator = typename std::vector<char>::const_iterator;
-    using source_ptr     = std::shared_ptr<const std::vector<char>>;
-
-    // delete default constructor. source_ never be null.
-    region() = delete;
-
-    explicit region(const location& loc)
-      : source_(loc.source()), source_name_(loc.name()),
-        first_(loc.iter()), last_(loc.iter())
-    {}
-    explicit region(location&& loc)
-      : source_(loc.source()), source_name_(loc.name()),
-        first_(loc.iter()), last_(loc.iter())
-    {}
-
-    region(const location& loc, const_iterator f, const_iterator l)
-      : source_(loc.source()), source_name_(loc.name()), first_(f), last_(l)
-    {}
-    region(location&& loc, const_iterator f, const_iterator l)
-      : source_(loc.source()), source_name_(loc.name()), first_(f), last_(l)
-    {}
-
-    region(const region&) = default;
-    region(region&&)      = default;
-    region& operator=(const region&) = default;
-    region& operator=(region&&)      = default;
-    ~region() = default;
-
-    region& operator+=(const region& other)
-    {
-        // different regions cannot be concatenated
-        assert(this->begin() == other.begin() && this->end() == other.end() &&
-               this->last_   == other.first_);
-
-        this->last_ = other.last_;
-        return *this;
-    }
-
-    bool is_ok() const noexcept override {return static_cast<bool>(source_);}
-    char front() const noexcept override {return *first_;}
-
-    std::string str()  const override {return make_string(first_, last_);}
-    std::string line() const override
-    {
-        if(this->contain_newline())
-        {
-            return make_string(this->line_begin(),
-                    std::find(this->line_begin(), this->last(), '\n'));
-        }
-        return make_string(this->line_begin(), this->line_end());
-    }
-    std::string line_num() const override
-    {
-        return std::to_string(1 + std::count(this->begin(), this->first(), '\n'));
-    }
-
-    std::size_t size() const noexcept override
-    {
-        const auto sz = std::distance(first_, last_);
-        assert(sz >= 0);
-        return static_cast<std::size_t>(sz);
-    }
-    std::size_t before() const noexcept override
-    {
-        const auto sz = std::distance(this->line_begin(), this->first());
-        assert(sz >= 0);
-        return static_cast<std::size_t>(sz);
-    }
-    std::size_t after() const noexcept override
-    {
-        const auto sz = std::distance(this->last(), this->line_end());
-        assert(sz >= 0);
-        return static_cast<std::size_t>(sz);
-    }
-
-    bool contain_newline() const noexcept
-    {
-        return std::find(this->first(), this->last(), '\n') != this->last();
-    }
-
-    const_iterator line_begin() const noexcept
-    {
-        using reverse_iterator = std::reverse_iterator<const_iterator>;
-        return std::find(reverse_iterator(this->first()),
-                         reverse_iterator(this->begin()), '\n').base();
-    }
-    const_iterator line_end() const noexcept
-    {
-        return std::find(this->last(), this->end(), '\n');
-    }
-
-    const_iterator begin() const noexcept {return source_->cbegin();}
-    const_iterator end()   const noexcept {return source_->cend();}
-    const_iterator first() const noexcept {return first_;}
-    const_iterator last()  const noexcept {return last_;}
-
-    source_ptr const& source() const& noexcept {return source_;}
-    source_ptr&&      source() &&     noexcept {return std::move(source_);}
-
-    std::string name() const override {return source_name_;}
-
-    std::vector<std::string> comments() const override
-    {
-        // assuming the current region (`*this`) points a value.
-        // ```toml
-        // a = "value"
-        //     ^^^^^^^- this region
-        // ```
-        using rev_iter = std::reverse_iterator<const_iterator>;
-
-        std::vector<std::string> com{};
-        {
-            // find comments just before the current region.
-            // ```toml
-            // # this should be collected.
-            // # this also.
-            // a = value # not this.
-            // ```
-
-            // # this is a comment for `a`, not array elements.
-            // a = [1, 2, 3, 4, 5]
-            if(this->first() == std::find_if(this->line_begin(), this->first(),
-                [](const char c) noexcept -> bool {return c == '[' || c == '{';}))
-            {
-                auto iter = this->line_begin(); // points the first character
-                while(iter != this->begin())
-                {
-                    iter = std::prev(iter);
-
-                    // range [line_start, iter) represents the previous line
-                    const auto line_start   = std::find(
-                            rev_iter(iter), rev_iter(this->begin()), '\n').base();
-                    const auto comment_found = std::find(line_start, iter, '#');
-                    if(comment_found == iter)
-                    {
-                        break; // comment not found.
-                    }
-
-                    // exclude the following case.
-                    // > a = "foo" # comment // <-- this is not a comment for b but a.
-                    // > b = "current value"
-                    if(std::all_of(line_start, comment_found,
-                            [](const char c) noexcept -> bool {
-                                return c == ' ' || c == '\t';
-                            }))
-                    {
-                        // unwrap the first '#' by std::next.
-                        auto s = make_string(std::next(comment_found), iter);
-                        if(!s.empty() && s.back() == '\r') {s.pop_back();}
-                        com.push_back(std::move(s));
-                    }
-                    else
-                    {
-                        break;
-                    }
-                    iter = line_start;
-                }
-            }
-        }
-
-        if(com.size() > 1)
-        {
-            std::reverse(com.begin(), com.end());
-        }
-
-        {
-            // find comments just after the current region.
-            // ```toml
-            // # not this.
-            // a = value # this one.
-            // a = [ # not this (technically difficult)
-            //
-            // ] # and this.
-            // ```
-            // The reason why it's difficult is that it requires parsing in the
-            // following case.
-            // ```toml
-            // a = [ 10 # this comment is for `10`. not for `a` but `a[0]`.
-            // # ...
-            // ] # this is apparently a comment for a.
-            //
-            // b = [
-            // 3.14 ] # there is no way to add a comment to `3.14` currently.
-            //
-            // c = [
-            //   3.14 # do this if you need a comment here.
-            // ]
-            // ```
-            const auto comment_found =
-                std::find(this->last(), this->line_end(), '#');
-            if(comment_found != this->line_end()) // '#' found
-            {
-                // table = {key = "value"} # what is this for?
-                // the above comment is not for "value", but {key="value"}.
-                if(comment_found == std::find_if(this->last(), comment_found,
-                    [](const char c) noexcept -> bool {
-                        return !(c == ' ' || c == '\t' || c == ',');
-                    }))
-                {
-                    // unwrap the first '#' by std::next.
-                    auto s = make_string(std::next(comment_found), this->line_end());
-                    if(!s.empty() && s.back() == '\r') {s.pop_back();}
-                    com.push_back(std::move(s));
-                }
-            }
-        }
-        return com;
-    }
-
-  private:
-
-    source_ptr     source_;
-    std::string    source_name_;
-    const_iterator first_, last_;
-};
-
-} // detail
-} // toml
-#endif// TOML11_REGION_H
diff --git a/src/toml11/toml/result.hpp b/src/toml11/toml/result.hpp
deleted file mode 100644
index 77cd46c64..000000000
--- a/src/toml11/toml/result.hpp
+++ /dev/null
@@ -1,717 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_RESULT_HPP
-#define TOML11_RESULT_HPP
-#include "traits.hpp"
-#include <type_traits>
-#include <stdexcept>
-#include <utility>
-#include <new>
-#include <string>
-#include <sstream>
-#include <cassert>
-
-namespace toml
-{
-
-template<typename T>
-struct success
-{
-    using value_type = T;
-    value_type value;
-
-    explicit success(const value_type& v)
-        noexcept(std::is_nothrow_copy_constructible<value_type>::value)
-        : value(v)
-    {}
-    explicit success(value_type&& v)
-        noexcept(std::is_nothrow_move_constructible<value_type>::value)
-        : value(std::move(v))
-    {}
-
-    template<typename U>
-    explicit success(U&& v): value(std::forward<U>(v)) {}
-
-    template<typename U>
-    explicit success(const success<U>& v): value(v.value) {}
-    template<typename U>
-    explicit success(success<U>&& v): value(std::move(v.value)) {}
-
-    ~success() = default;
-    success(const success&) = default;
-    success(success&&)      = default;
-    success& operator=(const success&) = default;
-    success& operator=(success&&)      = default;
-};
-
-template<typename T>
-struct failure
-{
-    using value_type = T;
-    value_type value;
-
-    explicit failure(const value_type& v)
-        noexcept(std::is_nothrow_copy_constructible<value_type>::value)
-        : value(v)
-    {}
-    explicit failure(value_type&& v)
-        noexcept(std::is_nothrow_move_constructible<value_type>::value)
-        : value(std::move(v))
-    {}
-
-    template<typename U>
-    explicit failure(U&& v): value(std::forward<U>(v)) {}
-
-    template<typename U>
-    explicit failure(const failure<U>& v): value(v.value) {}
-    template<typename U>
-    explicit failure(failure<U>&& v): value(std::move(v.value)) {}
-
-    ~failure() = default;
-    failure(const failure&) = default;
-    failure(failure&&)      = default;
-    failure& operator=(const failure&) = default;
-    failure& operator=(failure&&)      = default;
-};
-
-template<typename T>
-success<typename std::remove_cv<typename std::remove_reference<T>::type>::type>
-ok(T&& v)
-{
-    return success<
-        typename std::remove_cv<typename std::remove_reference<T>::type>::type
-        >(std::forward<T>(v));
-}
-template<typename T>
-failure<typename std::remove_cv<typename std::remove_reference<T>::type>::type>
-err(T&& v)
-{
-    return failure<
-        typename std::remove_cv<typename std::remove_reference<T>::type>::type
-        >(std::forward<T>(v));
-}
-
-inline success<std::string> ok(const char* literal)
-{
-    return success<std::string>(std::string(literal));
-}
-inline failure<std::string> err(const char* literal)
-{
-    return failure<std::string>(std::string(literal));
-}
-
-
-template<typename T, typename E>
-struct result
-{
-    using value_type = T;
-    using error_type = E;
-    using success_type = success<value_type>;
-    using failure_type = failure<error_type>;
-
-    result(const success_type& s): is_ok_(true)
-    {
-        auto tmp = ::new(std::addressof(this->succ)) success_type(s);
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-    }
-    result(const failure_type& f): is_ok_(false)
-    {
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(f);
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-    }
-    result(success_type&& s): is_ok_(true)
-    {
-        auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(s));
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-    }
-    result(failure_type&& f): is_ok_(false)
-    {
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(f));
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-    }
-
-    template<typename U>
-    result(const success<U>& s): is_ok_(true)
-    {
-        auto tmp = ::new(std::addressof(this->succ)) success_type(s.value);
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-    }
-    template<typename U>
-    result(const failure<U>& f): is_ok_(false)
-    {
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(f.value);
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-    }
-    template<typename U>
-    result(success<U>&& s): is_ok_(true)
-    {
-        auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(s.value));
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-    }
-    template<typename U>
-    result(failure<U>&& f): is_ok_(false)
-    {
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(f.value));
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-    }
-
-    result& operator=(const success_type& s)
-    {
-        this->cleanup();
-        this->is_ok_ = true;
-        auto tmp = ::new(std::addressof(this->succ)) success_type(s);
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-        return *this;
-    }
-    result& operator=(const failure_type& f)
-    {
-        this->cleanup();
-        this->is_ok_ = false;
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(f);
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-        return *this;
-    }
-    result& operator=(success_type&& s)
-    {
-        this->cleanup();
-        this->is_ok_ = true;
-        auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(s));
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-        return *this;
-    }
-    result& operator=(failure_type&& f)
-    {
-        this->cleanup();
-        this->is_ok_ = false;
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(f));
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-        return *this;
-    }
-
-    template<typename U>
-    result& operator=(const success<U>& s)
-    {
-        this->cleanup();
-        this->is_ok_ = true;
-        auto tmp = ::new(std::addressof(this->succ)) success_type(s.value);
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-        return *this;
-    }
-    template<typename U>
-    result& operator=(const failure<U>& f)
-    {
-        this->cleanup();
-        this->is_ok_ = false;
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(f.value);
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-        return *this;
-    }
-    template<typename U>
-    result& operator=(success<U>&& s)
-    {
-        this->cleanup();
-        this->is_ok_ = true;
-        auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(s.value));
-        assert(tmp == std::addressof(this->succ));
-        (void)tmp;
-        return *this;
-    }
-    template<typename U>
-    result& operator=(failure<U>&& f)
-    {
-        this->cleanup();
-        this->is_ok_ = false;
-        auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(f.value));
-        assert(tmp == std::addressof(this->fail));
-        (void)tmp;
-        return *this;
-    }
-
-    ~result() noexcept {this->cleanup();}
-
-    result(const result& other): is_ok_(other.is_ok())
-    {
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(other.as_ok());
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(other.as_err());
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-    }
-    result(result&& other): is_ok_(other.is_ok())
-    {
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(other.as_ok()));
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(other.as_err()));
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-    }
-
-    template<typename U, typename F>
-    result(const result<U, F>& other): is_ok_(other.is_ok())
-    {
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(other.as_ok());
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(other.as_err());
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-    }
-    template<typename U, typename F>
-    result(result<U, F>&& other): is_ok_(other.is_ok())
-    {
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(other.as_ok()));
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(other.as_err()));
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-    }
-
-    result& operator=(const result& other)
-    {
-        this->cleanup();
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(other.as_ok());
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(other.as_err());
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-        is_ok_ = other.is_ok();
-        return *this;
-    }
-    result& operator=(result&& other)
-    {
-        this->cleanup();
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(other.as_ok()));
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(other.as_err()));
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-        is_ok_ = other.is_ok();
-        return *this;
-    }
-
-    template<typename U, typename F>
-    result& operator=(const result<U, F>& other)
-    {
-        this->cleanup();
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(other.as_ok());
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(other.as_err());
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-        is_ok_ = other.is_ok();
-        return *this;
-    }
-    template<typename U, typename F>
-    result& operator=(result<U, F>&& other)
-    {
-        this->cleanup();
-        if(other.is_ok())
-        {
-            auto tmp = ::new(std::addressof(this->succ)) success_type(std::move(other.as_ok()));
-            assert(tmp == std::addressof(this->succ));
-            (void)tmp;
-        }
-        else
-        {
-            auto tmp = ::new(std::addressof(this->fail)) failure_type(std::move(other.as_err()));
-            assert(tmp == std::addressof(this->fail));
-            (void)tmp;
-        }
-        is_ok_ = other.is_ok();
-        return *this;
-    }
-
-    bool is_ok()  const noexcept {return is_ok_;}
-    bool is_err() const noexcept {return !is_ok_;}
-
-    operator bool() const noexcept {return is_ok_;}
-
-    value_type&       unwrap() &
-    {
-        if(is_err())
-        {
-            throw std::runtime_error("toml::result: bad unwrap: " +
-                                     format_error(this->as_err()));
-        }
-        return this->succ.value;
-    }
-    value_type const& unwrap() const&
-    {
-        if(is_err())
-        {
-            throw std::runtime_error("toml::result: bad unwrap: " +
-                                     format_error(this->as_err()));
-        }
-        return this->succ.value;
-    }
-    value_type&&      unwrap() &&
-    {
-        if(is_err())
-        {
-            throw std::runtime_error("toml::result: bad unwrap: " +
-                                     format_error(this->as_err()));
-        }
-        return std::move(this->succ.value);
-    }
-
-    value_type&       unwrap_or(value_type& opt) &
-    {
-        if(is_err()) {return opt;}
-        return this->succ.value;
-    }
-    value_type const& unwrap_or(value_type const& opt) const&
-    {
-        if(is_err()) {return opt;}
-        return this->succ.value;
-    }
-    value_type        unwrap_or(value_type opt) &&
-    {
-        if(is_err()) {return opt;}
-        return this->succ.value;
-    }
-
-    error_type&       unwrap_err() &
-    {
-        if(is_ok()) {throw std::runtime_error("toml::result: bad unwrap_err");}
-        return this->fail.value;
-    }
-    error_type const& unwrap_err() const&
-    {
-        if(is_ok()) {throw std::runtime_error("toml::result: bad unwrap_err");}
-        return this->fail.value;
-    }
-    error_type&&      unwrap_err() &&
-    {
-        if(is_ok()) {throw std::runtime_error("toml::result: bad unwrap_err");}
-        return std::move(this->fail.value);
-    }
-
-    value_type&       as_ok() &      noexcept {return this->succ.value;}
-    value_type const& as_ok() const& noexcept {return this->succ.value;}
-    value_type&&      as_ok() &&     noexcept {return std::move(this->succ.value);}
-
-    error_type&       as_err() &      noexcept {return this->fail.value;}
-    error_type const& as_err() const& noexcept {return this->fail.value;}
-    error_type&&      as_err() &&     noexcept {return std::move(this->fail.value);}
-
-
-    // prerequisities
-    // F: T -> U
-    // retval: result<U, E>
-    template<typename F>
-    result<detail::return_type_of_t<F, value_type&>, error_type>
-    map(F&& f) &
-    {
-        if(this->is_ok()){return ok(f(this->as_ok()));}
-        return err(this->as_err());
-    }
-    template<typename F>
-    result<detail::return_type_of_t<F, value_type const&>, error_type>
-    map(F&& f) const&
-    {
-        if(this->is_ok()){return ok(f(this->as_ok()));}
-        return err(this->as_err());
-    }
-    template<typename F>
-    result<detail::return_type_of_t<F, value_type &&>, error_type>
-    map(F&& f) &&
-    {
-        if(this->is_ok()){return ok(f(std::move(this->as_ok())));}
-        return err(std::move(this->as_err()));
-    }
-
-    // prerequisities
-    // F: E -> F
-    // retval: result<T, F>
-    template<typename F>
-    result<value_type, detail::return_type_of_t<F, error_type&>>
-    map_err(F&& f) &
-    {
-        if(this->is_err()){return err(f(this->as_err()));}
-        return ok(this->as_ok());
-    }
-    template<typename F>
-    result<value_type, detail::return_type_of_t<F, error_type const&>>
-    map_err(F&& f) const&
-    {
-        if(this->is_err()){return err(f(this->as_err()));}
-        return ok(this->as_ok());
-    }
-    template<typename F>
-    result<value_type, detail::return_type_of_t<F, error_type&&>>
-    map_err(F&& f) &&
-    {
-        if(this->is_err()){return err(f(std::move(this->as_err())));}
-        return ok(std::move(this->as_ok()));
-    }
-
-    // prerequisities
-    // F: T -> U
-    // retval: U
-    template<typename F, typename U>
-    detail::return_type_of_t<F, value_type&>
-    map_or_else(F&& f, U&& opt) &
-    {
-        if(this->is_err()){return std::forward<U>(opt);}
-        return f(this->as_ok());
-    }
-    template<typename F, typename U>
-    detail::return_type_of_t<F, value_type const&>
-    map_or_else(F&& f, U&& opt) const&
-    {
-        if(this->is_err()){return std::forward<U>(opt);}
-        return f(this->as_ok());
-    }
-    template<typename F, typename U>
-    detail::return_type_of_t<F, value_type&&>
-    map_or_else(F&& f, U&& opt) &&
-    {
-        if(this->is_err()){return std::forward<U>(opt);}
-        return f(std::move(this->as_ok()));
-    }
-
-    // prerequisities
-    // F: E -> U
-    // retval: U
-    template<typename F, typename U>
-    detail::return_type_of_t<F, error_type&>
-    map_err_or_else(F&& f, U&& opt) &
-    {
-        if(this->is_ok()){return std::forward<U>(opt);}
-        return f(this->as_err());
-    }
-    template<typename F, typename U>
-    detail::return_type_of_t<F, error_type const&>
-    map_err_or_else(F&& f, U&& opt) const&
-    {
-        if(this->is_ok()){return std::forward<U>(opt);}
-        return f(this->as_err());
-    }
-    template<typename F, typename U>
-    detail::return_type_of_t<F, error_type&&>
-    map_err_or_else(F&& f, U&& opt) &&
-    {
-        if(this->is_ok()){return std::forward<U>(opt);}
-        return f(std::move(this->as_err()));
-    }
-
-    // prerequisities:
-    // F: func T -> U
-    // toml::err(error_type) should be convertible to U.
-    // normally, type U is another result<S, F> and E is convertible to F
-    template<typename F>
-    detail::return_type_of_t<F, value_type&>
-    and_then(F&& f) &
-    {
-        if(this->is_ok()){return f(this->as_ok());}
-        return err(this->as_err());
-    }
-    template<typename F>
-    detail::return_type_of_t<F, value_type const&>
-    and_then(F&& f) const&
-    {
-        if(this->is_ok()){return f(this->as_ok());}
-        return err(this->as_err());
-    }
-    template<typename F>
-    detail::return_type_of_t<F, value_type&&>
-    and_then(F&& f) &&
-    {
-        if(this->is_ok()){return f(std::move(this->as_ok()));}
-        return err(std::move(this->as_err()));
-    }
-
-    // prerequisities:
-    // F: func E -> U
-    // toml::ok(value_type) should be convertible to U.
-    // normally, type U is another result<S, F> and T is convertible to S
-    template<typename F>
-    detail::return_type_of_t<F, error_type&>
-    or_else(F&& f) &
-    {
-        if(this->is_err()){return f(this->as_err());}
-        return ok(this->as_ok());
-    }
-    template<typename F>
-    detail::return_type_of_t<F, error_type const&>
-    or_else(F&& f) const&
-    {
-        if(this->is_err()){return f(this->as_err());}
-        return ok(this->as_ok());
-    }
-    template<typename F>
-    detail::return_type_of_t<F, error_type&&>
-    or_else(F&& f) &&
-    {
-        if(this->is_err()){return f(std::move(this->as_err()));}
-        return ok(std::move(this->as_ok()));
-    }
-
-    // if *this is error, returns *this. otherwise, returns other.
-    result and_other(const result& other) const&
-    {
-        return this->is_err() ? *this : other;
-    }
-    result and_other(result&& other) &&
-    {
-        return this->is_err() ? std::move(*this) : std::move(other);
-    }
-
-    // if *this is okay, returns *this. otherwise, returns other.
-    result or_other(const result& other) const&
-    {
-        return this->is_ok() ? *this : other;
-    }
-    result or_other(result&& other) &&
-    {
-        return this->is_ok() ? std::move(*this) : std::move(other);
-    }
-
-    void swap(result<T, E>& other)
-    {
-        result<T, E> tmp(std::move(*this));
-        *this = std::move(other);
-        other = std::move(tmp);
-        return ;
-    }
-
-  private:
-
-    static std::string format_error(std::exception const& excpt)
-    {
-        return std::string(excpt.what());
-    }
-    template<typename U, typename std::enable_if<!std::is_base_of<
-        std::exception, U>::value, std::nullptr_t>::type = nullptr>
-    static std::string format_error(U const& others)
-    {
-        std::ostringstream oss; oss << others;
-        return oss.str();
-    }
-
-    void cleanup() noexcept
-    {
-        if(this->is_ok_) {this->succ.~success_type();}
-        else             {this->fail.~failure_type();}
-        return;
-    }
-
-  private:
-
-    bool      is_ok_;
-    union
-    {
-        success_type succ;
-        failure_type fail;
-    };
-};
-
-template<typename T, typename E>
-void swap(result<T, E>& lhs, result<T, E>& rhs)
-{
-    lhs.swap(rhs);
-    return;
-}
-
-// this might be confusing because it eagerly evaluated, while in the other
-// cases operator && and || are short-circuited.
-//
-// template<typename T, typename E>
-// inline result<T, E>
-// operator&&(const result<T, E>& lhs, const result<T, E>& rhs) noexcept
-// {
-//     return lhs.is_ok() ? rhs : lhs;
-// }
-//
-// template<typename T, typename E>
-// inline result<T, E>
-// operator||(const result<T, E>& lhs, const result<T, E>& rhs) noexcept
-// {
-//     return lhs.is_ok() ? lhs : rhs;
-// }
-
-// ----------------------------------------------------------------------------
-// re-use result<T, E> as a optional<T> with none_t
-
-namespace detail
-{
-struct none_t {};
-inline bool operator==(const none_t&, const none_t&) noexcept {return true;}
-inline bool operator!=(const none_t&, const none_t&) noexcept {return false;}
-inline bool operator< (const none_t&, const none_t&) noexcept {return false;}
-inline bool operator<=(const none_t&, const none_t&) noexcept {return true;}
-inline bool operator> (const none_t&, const none_t&) noexcept {return false;}
-inline bool operator>=(const none_t&, const none_t&) noexcept {return true;}
-template<typename charT, typename traitsT>
-std::basic_ostream<charT, traitsT>&
-operator<<(std::basic_ostream<charT, traitsT>& os, const none_t&)
-{
-    os << "none";
-    return os;
-}
-inline failure<none_t> none() noexcept {return failure<none_t>{none_t{}};}
-} // detail
-} // toml11
-#endif// TOML11_RESULT_H
diff --git a/src/toml11/toml/serializer.hpp b/src/toml11/toml/serializer.hpp
deleted file mode 100644
index 88ae775a8..000000000
--- a/src/toml11/toml/serializer.hpp
+++ /dev/null
@@ -1,922 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_SERIALIZER_HPP
-#define TOML11_SERIALIZER_HPP
-#include <cmath>
-#include <cstdio>
-
-#include <limits>
-
-#include "lexer.hpp"
-#include "value.hpp"
-
-namespace toml
-{
-
-// This function serialize a key. It checks a string is a bare key and
-// escapes special characters if the string is not compatible to a bare key.
-// ```cpp
-// std::string k("non.bare.key"); // the key itself includes `.`s.
-// std::string formatted = toml::format_key(k);
-// assert(formatted == "\"non.bare.key\"");
-// ```
-//
-// This function is exposed to make it easy to write a user-defined serializer.
-// Since toml restricts characters available in a bare key, generally a string
-// should be escaped. But checking whether a string needs to be surrounded by
-// a `"` and escaping some special character is boring.
-template<typename charT, typename traits, typename Alloc>
-std::basic_string<charT, traits, Alloc>
-format_key(const std::basic_string<charT, traits, Alloc>& k)
-{
-    if(k.empty())
-    {
-        return std::string("\"\"");
-    }
-
-    // check the key can be a bare (unquoted) key
-    detail::location loc(k, std::vector<char>(k.begin(), k.end()));
-    detail::lex_unquoted_key::invoke(loc);
-    if(loc.iter() == loc.end())
-    {
-        return k; // all the tokens are consumed. the key is unquoted-key.
-    }
-
-    //if it includes special characters, then format it in a "quoted" key.
-    std::basic_string<charT, traits, Alloc> serialized("\"");
-    for(const char c : k)
-    {
-        switch(c)
-        {
-            case '\\': {serialized += "\\\\"; break;}
-            case '\"': {serialized += "\\\""; break;}
-            case '\b': {serialized += "\\b";  break;}
-            case '\t': {serialized += "\\t";  break;}
-            case '\f': {serialized += "\\f";  break;}
-            case '\n': {serialized += "\\n";  break;}
-            case '\r': {serialized += "\\r";  break;}
-            default  : {serialized += c;      break;}
-        }
-    }
-    serialized += "\"";
-    return serialized;
-}
-
-template<typename charT, typename traits, typename Alloc>
-std::basic_string<charT, traits, Alloc>
-format_keys(const std::vector<std::basic_string<charT, traits, Alloc>>& keys)
-{
-    if(keys.empty())
-    {
-        return std::string("\"\"");
-    }
-
-    std::basic_string<charT, traits, Alloc> serialized;
-    for(const auto& ky : keys)
-    {
-        serialized += format_key(ky);
-        serialized += charT('.');
-    }
-    serialized.pop_back(); // remove the last dot '.'
-    return serialized;
-}
-
-template<typename Value>
-struct serializer
-{
-    static_assert(detail::is_basic_value<Value>::value,
-                  "toml::serializer is for toml::value and its variants, "
-                  "toml::basic_value<...>.");
-
-    using value_type           = Value;
-    using key_type             = typename value_type::key_type            ;
-    using comment_type         = typename value_type::comment_type        ;
-    using boolean_type         = typename value_type::boolean_type        ;
-    using integer_type         = typename value_type::integer_type        ;
-    using floating_type        = typename value_type::floating_type       ;
-    using string_type          = typename value_type::string_type         ;
-    using local_time_type      = typename value_type::local_time_type     ;
-    using local_date_type      = typename value_type::local_date_type     ;
-    using local_datetime_type  = typename value_type::local_datetime_type ;
-    using offset_datetime_type = typename value_type::offset_datetime_type;
-    using array_type           = typename value_type::array_type          ;
-    using table_type           = typename value_type::table_type          ;
-
-    serializer(const std::size_t w              = 80u,
-               const int         float_prec     = std::numeric_limits<toml::floating>::max_digits10,
-               const bool        can_be_inlined = false,
-               const bool        no_comment     = false,
-               std::vector<toml::key> ks        = {},
-               const bool     value_has_comment = false)
-        : can_be_inlined_(can_be_inlined), no_comment_(no_comment),
-          value_has_comment_(value_has_comment && !no_comment),
-          float_prec_(float_prec), width_(w), keys_(std::move(ks))
-    {}
-    ~serializer() = default;
-
-    std::string operator()(const boolean_type& b) const
-    {
-        return b ? "true" : "false";
-    }
-    std::string operator()(const integer_type i) const
-    {
-        return std::to_string(i);
-    }
-    std::string operator()(const floating_type f) const
-    {
-        if(std::isnan(f))
-        {
-            if(std::signbit(f))
-            {
-                return std::string("-nan");
-            }
-            else
-            {
-                return std::string("nan");
-            }
-        }
-        else if(!std::isfinite(f))
-        {
-            if(std::signbit(f))
-            {
-                return std::string("-inf");
-            }
-            else
-            {
-                return std::string("inf");
-            }
-        }
-
-        const auto fmt = "%.*g";
-        const auto bsz = std::snprintf(nullptr, 0, fmt, this->float_prec_, f);
-        // +1 for null character(\0)
-        std::vector<char> buf(static_cast<std::size_t>(bsz + 1), '\0');
-        std::snprintf(buf.data(), buf.size(), fmt, this->float_prec_, f);
-
-        std::string token(buf.begin(), std::prev(buf.end()));
-        if(!token.empty() && token.back() == '.') // 1. => 1.0
-        {
-            token += '0';
-        }
-
-        const auto e = std::find_if(
-            token.cbegin(), token.cend(), [](const char c) noexcept -> bool {
-                return c == 'e' || c == 'E';
-            });
-        const auto has_exponent = (token.cend() != e);
-        const auto has_fraction = (token.cend() != std::find(
-            token.cbegin(), token.cend(), '.'));
-
-        if(!has_exponent && !has_fraction)
-        {
-            // the resulting value does not have any float specific part!
-            token += ".0";
-        }
-        return token;
-    }
-    std::string operator()(const string_type& s) const
-    {
-        if(s.kind == string_t::basic)
-        {
-            if((std::find(s.str.cbegin(), s.str.cend(), '\n') != s.str.cend() ||
-                std::find(s.str.cbegin(), s.str.cend(), '\"') != s.str.cend()) &&
-               this->width_ != (std::numeric_limits<std::size_t>::max)())
-            {
-                // if linefeed or double-quote is contained,
-                // make it multiline basic string.
-                const auto escaped = this->escape_ml_basic_string(s.str);
-                std::string open("\"\"\"");
-                std::string close("\"\"\"");
-                if(escaped.find('\n') != std::string::npos ||
-                   this->width_ < escaped.size() + 6)
-                {
-                    // if the string body contains newline or is enough long,
-                    // add newlines after and before delimiters.
-                    open += "\n";
-                    close = std::string("\\\n") + close;
-                }
-                return open + escaped + close;
-            }
-
-            // no linefeed. try to make it oneline-string.
-            std::string oneline = this->escape_basic_string(s.str);
-            if(oneline.size() + 2 < width_ || width_ < 2)
-            {
-                const std::string quote("\"");
-                return quote + oneline + quote;
-            }
-
-            // the line is too long compared to the specified width.
-            // split it into multiple lines.
-            std::string token("\"\"\"\n");
-            while(!oneline.empty())
-            {
-                if(oneline.size() < width_)
-                {
-                    token += oneline;
-                    oneline.clear();
-                }
-                else if(oneline.at(width_-2) == '\\')
-                {
-                    token += oneline.substr(0, width_-2);
-                    token += "\\\n";
-                    oneline.erase(0, width_-2);
-                }
-                else
-                {
-                    token += oneline.substr(0, width_-1);
-                    token += "\\\n";
-                    oneline.erase(0, width_-1);
-                }
-            }
-            return token + std::string("\\\n\"\"\"");
-        }
-        else // the string `s` is literal-string.
-        {
-            if(std::find(s.str.cbegin(), s.str.cend(), '\n') != s.str.cend() ||
-               std::find(s.str.cbegin(), s.str.cend(), '\'') != s.str.cend() )
-            {
-                std::string open("'''");
-                if(this->width_ + 6 < s.str.size())
-                {
-                    open += '\n'; // the first newline is ignored by TOML spec
-                }
-                const std::string close("'''");
-                return open + s.str + close;
-            }
-            else
-            {
-                const std::string quote("'");
-                return quote + s.str + quote;
-            }
-        }
-    }
-
-    std::string operator()(const local_date_type& d) const
-    {
-        std::ostringstream oss;
-        oss << d;
-        return oss.str();
-    }
-    std::string operator()(const local_time_type& t) const
-    {
-        std::ostringstream oss;
-        oss << t;
-        return oss.str();
-    }
-    std::string operator()(const local_datetime_type& dt) const
-    {
-        std::ostringstream oss;
-        oss << dt;
-        return oss.str();
-    }
-    std::string operator()(const offset_datetime_type& odt) const
-    {
-        std::ostringstream oss;
-        oss << odt;
-        return oss.str();
-    }
-
-    std::string operator()(const array_type& v) const
-    {
-        if(v.empty())
-        {
-            return std::string("[]");
-        }
-        if(this->is_array_of_tables(v))
-        {
-            return make_array_of_tables(v);
-        }
-
-        // not an array of tables. normal array.
-        // first, try to make it inline if none of the elements have a comment.
-        if( ! this->has_comment_inside(v))
-        {
-            const auto inl = this->make_inline_array(v);
-            if(inl.size() < this->width_ &&
-               std::find(inl.cbegin(), inl.cend(), '\n') == inl.cend())
-            {
-                return inl;
-            }
-        }
-
-        // if the length exceeds this->width_, print multiline array.
-        // key = [
-        //   # ...
-        //   42,
-        //   ...
-        // ]
-        std::string token;
-        std::string current_line;
-        token += "[\n";
-        for(const auto& item : v)
-        {
-            if( ! item.comments().empty() && !no_comment_)
-            {
-                // if comment exists, the element must be the only element in the line.
-                // e.g. the following is not allowed.
-                // ```toml
-                // array = [
-                // # comment for what?
-                // 1, 2, 3, 4, 5
-                // ]
-                // ```
-                if(!current_line.empty())
-                {
-                    if(current_line.back() != '\n')
-                    {
-                        current_line += '\n';
-                    }
-                    token += current_line;
-                    current_line.clear();
-                }
-                for(const auto& c : item.comments())
-                {
-                    token += '#';
-                    token += c;
-                    token += '\n';
-                }
-                token += toml::visit(*this, item);
-                if(!token.empty() && token.back() == '\n') {token.pop_back();}
-                token += ",\n";
-                continue;
-            }
-            std::string next_elem;
-            if(item.is_table())
-            {
-                serializer ser(*this);
-                ser.can_be_inlined_ = true;
-                ser.width_ = (std::numeric_limits<std::size_t>::max)();
-                next_elem += toml::visit(ser, item);
-            }
-            else
-            {
-                next_elem += toml::visit(*this, item);
-            }
-
-            // comma before newline.
-            if(!next_elem.empty() && next_elem.back() == '\n') {next_elem.pop_back();}
-
-            // if current line does not exceeds the width limit, continue.
-            if(current_line.size() + next_elem.size() + 1 < this->width_)
-            {
-                current_line += next_elem;
-                current_line += ',';
-            }
-            else if(current_line.empty())
-            {
-                // if current line was empty, force put the next_elem because
-                // next_elem is not splittable
-                token += next_elem;
-                token += ",\n";
-                // current_line is kept empty
-            }
-            else // reset current_line
-            {
-                assert(current_line.back() == ',');
-                token += current_line;
-                token += '\n';
-                current_line = next_elem;
-                current_line += ',';
-            }
-        }
-        if(!current_line.empty())
-        {
-            if(!current_line.empty() && current_line.back() != '\n')
-            {
-                current_line += '\n';
-            }
-            token += current_line;
-        }
-        token += "]\n";
-        return token;
-    }
-
-    // templatize for any table-like container
-    std::string operator()(const table_type& v) const
-    {
-        // if an element has a comment, then it can't be inlined.
-        // table = {# how can we write a comment for this? key = "value"}
-        if(this->can_be_inlined_ && !(this->has_comment_inside(v)))
-        {
-            std::string token;
-            if(!this->keys_.empty())
-            {
-                token += format_key(this->keys_.back());
-                token += " = ";
-            }
-            token += this->make_inline_table(v);
-            if(token.size() < this->width_ &&
-               token.end() == std::find(token.begin(), token.end(), '\n'))
-            {
-                return token;
-            }
-        }
-
-        std::string token;
-        if(!keys_.empty())
-        {
-            token += '[';
-            token += format_keys(keys_);
-            token += "]\n";
-        }
-        token += this->make_multiline_table(v);
-        return token;
-    }
-
-  private:
-
-    std::string escape_basic_string(const std::string& s) const
-    {
-        //XXX assuming `s` is a valid utf-8 sequence.
-        std::string retval;
-        for(const char c : s)
-        {
-            switch(c)
-            {
-                case '\\': {retval += "\\\\"; break;}
-                case '\"': {retval += "\\\""; break;}
-                case '\b': {retval += "\\b";  break;}
-                case '\t': {retval += "\\t";  break;}
-                case '\f': {retval += "\\f";  break;}
-                case '\n': {retval += "\\n";  break;}
-                case '\r': {retval += "\\r";  break;}
-                default  :
-                {
-                    if((0x00 <= c && c <= 0x08) || (0x0A <= c && c <= 0x1F) || c == 0x7F)
-                    {
-                        retval += "\\u00";
-                        retval += char(48 + (c / 16));
-                        retval += char((c % 16 < 10 ? 48 : 55) + (c % 16));
-                    }
-                    else
-                    {
-                        retval += c;
-                    }
-                }
-            }
-        }
-        return retval;
-    }
-
-    std::string escape_ml_basic_string(const std::string& s) const
-    {
-        std::string retval;
-        for(auto i=s.cbegin(), e=s.cend(); i!=e; ++i)
-        {
-            switch(*i)
-            {
-                case '\\': {retval += "\\\\"; break;}
-                // One or two consecutive "s are allowed.
-                // Later we will check there are no three consecutive "s.
-                //   case '\"': {retval += "\\\""; break;}
-                case '\b': {retval += "\\b";  break;}
-                case '\t': {retval += "\\t";  break;}
-                case '\f': {retval += "\\f";  break;}
-                case '\n': {retval += "\n";   break;}
-                case '\r':
-                {
-                    if(std::next(i) != e && *std::next(i) == '\n')
-                    {
-                        retval += "\r\n";
-                        ++i;
-                    }
-                    else
-                    {
-                        retval += "\\r";
-                    }
-                    break;
-                }
-                default  :
-                {
-                    const auto c = *i;
-                    if((0x00 <= c && c <= 0x08) || (0x0A <= c && c <= 0x1F) || c == 0x7F)
-                    {
-                        retval += "\\u00";
-                        retval += char(48 + (c / 16));
-                        retval += char((c % 16 < 10 ? 48 : 55) + (c % 16));
-                    }
-                    else
-                    {
-                        retval += c;
-                    }
-                }
-
-            }
-        }
-        // Only 1 or 2 consecutive `"`s are allowed in multiline basic string.
-        // 3 consecutive `"`s are considered as a closing delimiter.
-        // We need to check if there are 3 or more consecutive `"`s and insert
-        // backslash to break them down into several short `"`s like the `str6`
-        // in the following example.
-        // ```toml
-        // str4 = """Here are two quotation marks: "". Simple enough."""
-        // # str5 = """Here are three quotation marks: """."""  # INVALID
-        // str5 = """Here are three quotation marks: ""\"."""
-        // str6 = """Here are fifteen quotation marks: ""\"""\"""\"""\"""\"."""
-        // ```
-        auto found_3_quotes = retval.find("\"\"\"");
-        while(found_3_quotes != std::string::npos)
-        {
-            retval.replace(found_3_quotes, 3, "\"\"\\\"");
-            found_3_quotes = retval.find("\"\"\"");
-        }
-        return retval;
-    }
-
-    // if an element of a table or an array has a comment, it cannot be inlined.
-    bool has_comment_inside(const array_type& a) const noexcept
-    {
-        // if no_comment is set, comments would not be written.
-        if(this->no_comment_) {return false;}
-
-        for(const auto& v : a)
-        {
-            if(!v.comments().empty()) {return true;}
-        }
-        return false;
-    }
-    bool has_comment_inside(const table_type& t) const noexcept
-    {
-        // if no_comment is set, comments would not be written.
-        if(this->no_comment_) {return false;}
-
-        for(const auto& kv : t)
-        {
-            if(!kv.second.comments().empty()) {return true;}
-        }
-        return false;
-    }
-
-    std::string make_inline_array(const array_type& v) const
-    {
-        assert(!has_comment_inside(v));
-        std::string token;
-        token += '[';
-        bool is_first = true;
-        for(const auto& item : v)
-        {
-            if(is_first) {is_first = false;} else {token += ',';}
-            token += visit(serializer(
-                (std::numeric_limits<std::size_t>::max)(), this->float_prec_,
-                /* inlined */ true, /*no comment*/ false, /*keys*/ {},
-                /*has_comment*/ !item.comments().empty()), item);
-        }
-        token += ']';
-        return token;
-    }
-
-    std::string make_inline_table(const table_type& v) const
-    {
-        assert(!has_comment_inside(v));
-        assert(this->can_be_inlined_);
-        std::string token;
-        token += '{';
-        bool is_first = true;
-        for(const auto& kv : v)
-        {
-            // in inline tables, trailing comma is not allowed (toml-lang #569).
-            if(is_first) {is_first = false;} else {token += ',';}
-            token += format_key(kv.first);
-            token += '=';
-            token += visit(serializer(
-                (std::numeric_limits<std::size_t>::max)(), this->float_prec_,
-                /* inlined */ true, /*no comment*/ false, /*keys*/ {},
-                /*has_comment*/ !kv.second.comments().empty()), kv.second);
-        }
-        token += '}';
-        return token;
-    }
-
-    std::string make_multiline_table(const table_type& v) const
-    {
-        std::string token;
-
-        // print non-table elements first.
-        // ```toml
-        // [foo]         # a table we're writing now here
-        // key = "value" # <- non-table element, "key"
-        // # ...
-        // [foo.bar] # <- table element, "bar"
-        // ```
-        // because after printing [foo.bar], the remaining non-table values will
-        // be assigned into [foo.bar], not [foo]. Those values should be printed
-        // earlier.
-        for(const auto& kv : v)
-        {
-            if(kv.second.is_table() || is_array_of_tables(kv.second))
-            {
-                continue;
-            }
-
-            token += write_comments(kv.second);
-
-            const auto key_and_sep    = format_key(kv.first) + " = ";
-            const auto residual_width = (this->width_ > key_and_sep.size()) ?
-                                        this->width_ - key_and_sep.size() : 0;
-            token += key_and_sep;
-            token += visit(serializer(residual_width, this->float_prec_,
-                /*can be inlined*/ true, /*no comment*/ false, /*keys*/ {},
-                /*has_comment*/ !kv.second.comments().empty()), kv.second);
-
-            if(token.back() != '\n')
-            {
-                token += '\n';
-            }
-        }
-
-        // normal tables / array of tables
-
-        // after multiline table appeared, the other tables cannot be inline
-        // because the table would be assigned into the table.
-        // [foo]
-        // ...
-        // bar = {...} # <- bar will be a member of [foo].
-        bool multiline_table_printed = false;
-        for(const auto& kv : v)
-        {
-            if(!kv.second.is_table() && !is_array_of_tables(kv.second))
-            {
-                continue; // other stuff are already serialized. skip them.
-            }
-
-            std::vector<toml::key> ks(this->keys_);
-            ks.push_back(kv.first);
-
-            auto tmp = visit(serializer(this->width_, this->float_prec_,
-                !multiline_table_printed, this->no_comment_, ks,
-                /*has_comment*/ !kv.second.comments().empty()), kv.second);
-
-            // If it is the first time to print a multi-line table, it would be
-            // helpful to separate normal key-value pair and subtables by a
-            // newline.
-            // (this checks if the current key-value pair contains newlines.
-            //  but it is not perfect because multi-line string can also contain
-            //  a newline. in such a case, an empty line will be written) TODO
-            if((!multiline_table_printed) &&
-               std::find(tmp.cbegin(), tmp.cend(), '\n') != tmp.cend())
-            {
-                multiline_table_printed = true;
-                token += '\n'; // separate key-value pairs and subtables
-
-                token += write_comments(kv.second);
-                token += tmp;
-
-                // care about recursive tables (all tables in each level prints
-                // newline and there will be a full of newlines)
-                if(tmp.substr(tmp.size() - 2, 2) != "\n\n" &&
-                   tmp.substr(tmp.size() - 4, 4) != "\r\n\r\n" )
-                {
-                    token += '\n';
-                }
-            }
-            else
-            {
-                token += write_comments(kv.second);
-                token += tmp;
-                token += '\n';
-            }
-        }
-        return token;
-    }
-
-    std::string make_array_of_tables(const array_type& v) const
-    {
-        // if it's not inlined, we need to add `[[table.key]]`.
-        // but if it can be inlined, we can format it as the following.
-        // ```
-        // table.key = [
-        //   {...},
-        //   # comment
-        //   {...},
-        // ]
-        // ```
-        // This function checks if inlinization is possible or not, and then
-        // format the array-of-tables in a proper way.
-        //
-        // Note about comments:
-        //
-        // If the array itself has a comment (value_has_comment_ == true), we
-        // should try to make it inline.
-        // ```toml
-        // # comment about array
-        // array = [
-        //   # comment about table element
-        //   {of = "table"}
-        // ]
-        // ```
-        // If it is formatted as a multiline table, the two comments becomes
-        // indistinguishable.
-        // ```toml
-        // # comment about array
-        // # comment about table element
-        // [[array]]
-        // of = "table"
-        // ```
-        // So we need to try to make it inline, and it force-inlines regardless
-        // of the line width limit.
-        //     It may fail if the element of a table has comment. In that case,
-        // the array-of-tables will be formatted as a multiline table.
-        if(this->can_be_inlined_ || this->value_has_comment_)
-        {
-            std::string token;
-            if(!keys_.empty())
-            {
-                token += format_key(keys_.back());
-                token += " = ";
-            }
-
-            bool failed = false;
-            token += "[\n";
-            for(const auto& item : v)
-            {
-                // if an element of the table has a comment, the table
-                // cannot be inlined.
-                if(this->has_comment_inside(item.as_table()))
-                {
-                    failed = true;
-                    break;
-                }
-                // write comments for the table itself
-                token += write_comments(item);
-
-                const auto t = this->make_inline_table(item.as_table());
-
-                if(t.size() + 1 > width_ || // +1 for the last comma {...},
-                   std::find(t.cbegin(), t.cend(), '\n') != t.cend())
-                {
-                    // if the value itself has a comment, ignore the line width limit
-                    if( ! this->value_has_comment_)
-                    {
-                        failed = true;
-                        break;
-                    }
-                }
-                token += t;
-                token += ",\n";
-            }
-
-            if( ! failed)
-            {
-                token += "]\n";
-                return token;
-            }
-            // if failed, serialize them as [[array.of.tables]].
-        }
-
-        std::string token;
-        for(const auto& item : v)
-        {
-            token += write_comments(item);
-            token += "[[";
-            token += format_keys(keys_);
-            token += "]]\n";
-            token += this->make_multiline_table(item.as_table());
-        }
-        return token;
-    }
-
-    std::string write_comments(const value_type& v) const
-    {
-        std::string retval;
-        if(this->no_comment_) {return retval;}
-
-        for(const auto& c : v.comments())
-        {
-            retval += '#';
-            retval += c;
-            retval += '\n';
-        }
-        return retval;
-    }
-
-    bool is_array_of_tables(const value_type& v) const
-    {
-        if(!v.is_array() || v.as_array().empty()) {return false;}
-        return is_array_of_tables(v.as_array());
-    }
-    bool is_array_of_tables(const array_type& v) const
-    {
-        // Since TOML v0.5.0, heterogeneous arrays are allowed. So we need to
-        // check all the element in an array to check if the array is an array
-        // of tables.
-        return std::all_of(v.begin(), v.end(), [](const value_type& elem) {
-                return elem.is_table();
-            });
-    }
-
-  private:
-
-    bool        can_be_inlined_;
-    bool        no_comment_;
-    bool        value_has_comment_;
-    int         float_prec_;
-    std::size_t width_;
-    std::vector<toml::key> keys_;
-};
-
-template<typename C,
-         template<typename ...> class M, template<typename ...> class V>
-std::string
-format(const basic_value<C, M, V>& v, std::size_t w = 80u,
-       int fprec = std::numeric_limits<toml::floating>::max_digits10,
-       bool no_comment = false, bool force_inline = false)
-{
-    using value_type = basic_value<C, M, V>;
-    // if value is a table, it is considered to be a root object.
-    // the root object can't be an inline table.
-    if(v.is_table())
-    {
-        std::ostringstream oss;
-        if(!v.comments().empty())
-        {
-            oss << v.comments();
-            oss << '\n'; // to split the file comment from the first element
-        }
-        const auto serialized = visit(serializer<value_type>(w, fprec, false, no_comment), v);
-        oss << serialized;
-        return oss.str();
-    }
-    return visit(serializer<value_type>(w, fprec, force_inline), v);
-}
-
-namespace detail
-{
-template<typename charT, typename traits>
-int comment_index(std::basic_ostream<charT, traits>&)
-{
-    static const int index = std::ios_base::xalloc();
-    return index;
-}
-} // detail
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-nocomment(std::basic_ostream<charT, traits>& os)
-{
-    // by default, it is zero. and by default, it shows comments.
-    os.iword(detail::comment_index(os)) = 1;
-    return os;
-}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-showcomment(std::basic_ostream<charT, traits>& os)
-{
-    // by default, it is zero. and by default, it shows comments.
-    os.iword(detail::comment_index(os)) = 0;
-    return os;
-}
-
-template<typename charT, typename traits, typename C,
-         template<typename ...> class M, template<typename ...> class V>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const basic_value<C, M, V>& v)
-{
-    using value_type = basic_value<C, M, V>;
-
-    // get status of std::setw().
-    const auto w     = static_cast<std::size_t>(os.width());
-    const int  fprec = static_cast<int>(os.precision());
-    os.width(0);
-
-    // by default, iword is initialized by 0. And by default, toml11 outputs
-    // comments. So `0` means showcomment. 1 means nocommnet.
-    const bool no_comment = (1 == os.iword(detail::comment_index(os)));
-
-    if(!no_comment && v.is_table() && !v.comments().empty())
-    {
-        os << v.comments();
-        os << '\n'; // to split the file comment from the first element
-    }
-    // the root object can't be an inline table. so pass `false`.
-    const auto serialized = visit(serializer<value_type>(w, fprec, no_comment, false), v);
-    os << serialized;
-
-    // if v is a non-table value, and has only one comment, then
-    // put a comment just after a value. in the following way.
-    //
-    // ```toml
-    // key = "value" # comment.
-    // ```
-    //
-    // Since the top-level toml object is a table, one who want to put a
-    // non-table toml value must use this in a following way.
-    //
-    // ```cpp
-    // toml::value v;
-    // std::cout << "user-defined-key = " << v << std::endl;
-    // ```
-    //
-    // In this case, it is impossible to put comments before key-value pair.
-    // The only way to preserve comments is to put all of them after a value.
-    if(!no_comment && !v.is_table() && !v.comments().empty())
-    {
-        os << " #";
-        for(const auto& c : v.comments()) {os << c;}
-    }
-    return os;
-}
-
-} // toml
-#endif// TOML11_SERIALIZER_HPP
diff --git a/src/toml11/toml/source_location.hpp b/src/toml11/toml/source_location.hpp
deleted file mode 100644
index fa175b5b4..000000000
--- a/src/toml11/toml/source_location.hpp
+++ /dev/null
@@ -1,233 +0,0 @@
-//     Copyright Toru Niina 2019.
-// Distributed under the MIT License.
-#ifndef TOML11_SOURCE_LOCATION_HPP
-#define TOML11_SOURCE_LOCATION_HPP
-#include <cstdint>
-#include <sstream>
-
-#include "region.hpp"
-
-namespace toml
-{
-
-// A struct to contain location in a toml file.
-// The interface imitates std::experimental::source_location,
-// but not completely the same.
-//
-// It would be constructed by toml::value. It can be used to generate
-// user-defined error messages.
-//
-// - std::uint_least32_t line() const noexcept
-//   - returns the line number where the region is on.
-// - std::uint_least32_t column() const noexcept
-//   - returns the column number where the region starts.
-// - std::uint_least32_t region() const noexcept
-//   - returns the size of the region.
-//
-// +-- line()       +-- region of interest (region() == 9)
-// v            .---+---.
-// 12 | value = "foo bar"
-//              ^
-//              +-- column()
-//
-// - std::string const& file_name() const noexcept;
-//   - name of the file.
-// - std::string const& line_str() const noexcept;
-//   - the whole line that contains the region of interest.
-//
-struct source_location
-{
-  public:
-
-    source_location()
-        : line_num_(1), column_num_(1), region_size_(1),
-          file_name_("unknown file"), line_str_("")
-    {}
-
-    explicit source_location(const detail::region_base* reg)
-        : line_num_(1), column_num_(1), region_size_(1),
-          file_name_("unknown file"), line_str_("")
-    {
-        if(reg)
-        {
-            if(reg->line_num() != detail::region_base().line_num())
-            {
-                line_num_ = static_cast<std::uint_least32_t>(
-                        std::stoul(reg->line_num()));
-            }
-            column_num_  = static_cast<std::uint_least32_t>(reg->before() + 1);
-            region_size_ = static_cast<std::uint_least32_t>(reg->size());
-            file_name_   = reg->name();
-            line_str_    = reg->line();
-        }
-    }
-
-    explicit source_location(const detail::region& reg)
-        : line_num_(static_cast<std::uint_least32_t>(std::stoul(reg.line_num()))),
-          column_num_(static_cast<std::uint_least32_t>(reg.before() + 1)),
-          region_size_(static_cast<std::uint_least32_t>(reg.size())),
-          file_name_(reg.name()),
-          line_str_ (reg.line())
-    {}
-    explicit source_location(const detail::location& loc)
-        : line_num_(static_cast<std::uint_least32_t>(std::stoul(loc.line_num()))),
-          column_num_(static_cast<std::uint_least32_t>(loc.before() + 1)),
-          region_size_(static_cast<std::uint_least32_t>(loc.size())),
-          file_name_(loc.name()),
-          line_str_ (loc.line())
-    {}
-
-    ~source_location() = default;
-    source_location(source_location const&) = default;
-    source_location(source_location &&)     = default;
-    source_location& operator=(source_location const&) = default;
-    source_location& operator=(source_location &&)     = default;
-
-    std::uint_least32_t line()      const noexcept {return line_num_;}
-    std::uint_least32_t column()    const noexcept {return column_num_;}
-    std::uint_least32_t region()    const noexcept {return region_size_;}
-
-    std::string const&  file_name() const noexcept {return file_name_;}
-    std::string const&  line_str()  const noexcept {return line_str_;}
-
-  private:
-
-    std::uint_least32_t line_num_;
-    std::uint_least32_t column_num_;
-    std::uint_least32_t region_size_;
-    std::string         file_name_;
-    std::string         line_str_;
-};
-
-namespace detail
-{
-
-// internal error message generation.
-inline std::string format_underline(const std::string& message,
-        const std::vector<std::pair<source_location, std::string>>& loc_com,
-        const std::vector<std::string>& helps = {},
-        const bool colorize = TOML11_ERROR_MESSAGE_COLORIZED)
-{
-    std::size_t line_num_width = 0;
-    for(const auto& lc : loc_com)
-    {
-        std::uint_least32_t line = lc.first.line();
-        std::size_t        digit = 0;
-        while(line != 0)
-        {
-            line  /= 10;
-            digit +=  1;
-        }
-        line_num_width = (std::max)(line_num_width, digit);
-    }
-    // 1 is the minimum width
-    line_num_width = std::max<std::size_t>(line_num_width, 1);
-
-    std::ostringstream retval;
-
-    if(colorize)
-    {
-        retval << color::colorize; // turn on ANSI color
-    }
-
-    // XXX
-    // Here, before `colorize` support, it does not output `[error]` prefix
-    // automatically. So some user may output it manually and this change may
-    // duplicate the prefix. To avoid it, check the first 7 characters and
-    // if it is "[error]", it removes that part from the message shown.
-    if(message.size() > 7 && message.substr(0, 7) == "[error]")
-    {
-        retval << color::bold << color::red << "[error]" << color::reset
-               << color::bold << message.substr(7) << color::reset << '\n';
-    }
-    else
-    {
-        retval << color::bold << color::red << "[error] " << color::reset
-               << color::bold << message << color::reset << '\n';
-    }
-
-    const auto format_one_location = [line_num_width]
-        (std::ostringstream& oss,
-         const source_location& loc, const std::string& comment) -> void
-        {
-            oss << ' ' << color::bold << color::blue
-                << std::setw(static_cast<int>(line_num_width))
-                << std::right << loc.line() << " | "  << color::reset
-                << loc.line_str() << '\n';
-
-            oss << make_string(line_num_width + 1, ' ')
-                << color::bold << color::blue << " | " << color::reset
-                << make_string(loc.column()-1 /*1-origin*/, ' ');
-
-            if(loc.region() == 1)
-            {
-                // invalid
-                // ^------
-                oss << color::bold << color::red << "^---" << color::reset;
-            }
-            else
-            {
-                // invalid
-                // ~~~~~~~
-                const auto underline_len = (std::min)(
-                    static_cast<std::size_t>(loc.region()), loc.line_str().size());
-                oss << color::bold << color::red
-                    << make_string(underline_len, '~') << color::reset;
-            }
-            oss << ' ';
-            oss << comment;
-            return;
-        };
-
-    assert(!loc_com.empty());
-
-    // --> example.toml
-    //   |
-    retval << color::bold << color::blue << " --> " << color::reset
-           << loc_com.front().first.file_name() << '\n';
-    retval << make_string(line_num_width + 1, ' ')
-           << color::bold << color::blue << " |\n"  << color::reset;
-    // 1 | key value
-    //   |    ^--- missing =
-    format_one_location(retval, loc_com.front().first, loc_com.front().second);
-
-    // process the rest of the locations
-    for(std::size_t i=1; i<loc_com.size(); ++i)
-    {
-        const auto& prev = loc_com.at(i-1);
-        const auto& curr = loc_com.at(i);
-
-        retval << '\n';
-        // if the filenames are the same, print "..."
-        if(prev.first.file_name() == curr.first.file_name())
-        {
-            retval << color::bold << color::blue << " ...\n" << color::reset;
-        }
-        else // if filename differs, print " --> filename.toml" again
-        {
-            retval << color::bold << color::blue << " --> " << color::reset
-                   << curr.first.file_name() << '\n';
-            retval << make_string(line_num_width + 1, ' ')
-                   << color::bold << color::blue << " |\n"  << color::reset;
-        }
-
-        format_one_location(retval, curr.first, curr.second);
-    }
-
-    if(!helps.empty())
-    {
-        retval << '\n';
-        retval << make_string(line_num_width + 1, ' ');
-        retval << color::bold << color::blue << " |" << color::reset;
-        for(const auto& help : helps)
-        {
-            retval << color::bold << "\nHint: " << color::reset;
-            retval << help;
-        }
-    }
-    return retval.str();
-}
-
-} // detail
-} // toml
-#endif// TOML11_SOURCE_LOCATION_HPP
diff --git a/src/toml11/toml/storage.hpp b/src/toml11/toml/storage.hpp
deleted file mode 100644
index 202f9035f..000000000
--- a/src/toml11/toml/storage.hpp
+++ /dev/null
@@ -1,43 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_STORAGE_HPP
-#define TOML11_STORAGE_HPP
-#include "utility.hpp"
-
-namespace toml
-{
-namespace detail
-{
-
-// this contains pointer and deep-copy the content if copied.
-// to avoid recursive pointer.
-template<typename T>
-struct storage
-{
-    using value_type = T;
-
-    explicit storage(value_type const& v): ptr(toml::make_unique<T>(v)) {}
-    explicit storage(value_type&&      v): ptr(toml::make_unique<T>(std::move(v))) {}
-    ~storage() = default;
-    storage(const storage& rhs): ptr(toml::make_unique<T>(*rhs.ptr)) {}
-    storage& operator=(const storage& rhs)
-    {
-        this->ptr = toml::make_unique<T>(*rhs.ptr);
-        return *this;
-    }
-    storage(storage&&) = default;
-    storage& operator=(storage&&) = default;
-
-    bool is_ok() const noexcept {return static_cast<bool>(ptr);}
-
-    value_type&       value() &      noexcept {return *ptr;}
-    value_type const& value() const& noexcept {return *ptr;}
-    value_type&&      value() &&     noexcept {return std::move(*ptr);}
-
-  private:
-    std::unique_ptr<value_type> ptr;
-};
-
-} // detail
-} // toml
-#endif// TOML11_STORAGE_HPP
diff --git a/src/toml11/toml/string.hpp b/src/toml11/toml/string.hpp
deleted file mode 100644
index 5136d8c56..000000000
--- a/src/toml11/toml/string.hpp
+++ /dev/null
@@ -1,225 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_STRING_HPP
-#define TOML11_STRING_HPP
-#include <cstdint>
-
-#include <algorithm>
-#include <string>
-
-#if __cplusplus >= 201703L
-#if __has_include(<string_view>)
-#define TOML11_USING_STRING_VIEW 1
-#include <string_view>
-#endif
-#endif
-
-namespace toml
-{
-
-enum class string_t : std::uint8_t
-{
-    basic   = 0,
-    literal = 1,
-};
-
-struct string
-{
-    string()  = default;
-    ~string() = default;
-    string(const string& s) = default;
-    string(string&& s)      = default;
-    string& operator=(const string& s) = default;
-    string& operator=(string&& s)      = default;
-
-    string(const std::string& s): kind(string_t::basic), str(s){}
-    string(const std::string& s, string_t k):   kind(k), str(s){}
-    string(const char* s):        kind(string_t::basic), str(s){}
-    string(const char* s,        string_t k):   kind(k), str(s){}
-
-    string(std::string&& s): kind(string_t::basic), str(std::move(s)){}
-    string(std::string&& s, string_t k):   kind(k), str(std::move(s)){}
-
-    string& operator=(const std::string& s)
-    {kind = string_t::basic; str = s; return *this;}
-    string& operator=(std::string&& s)
-    {kind = string_t::basic; str = std::move(s); return *this;}
-
-    operator std::string&       () &      noexcept {return str;}
-    operator std::string const& () const& noexcept {return str;}
-    operator std::string&&      () &&     noexcept {return std::move(str);}
-
-    string& operator+=(const char*        rhs) {str += rhs; return *this;}
-    string& operator+=(const char         rhs) {str += rhs; return *this;}
-    string& operator+=(const std::string& rhs) {str += rhs; return *this;}
-    string& operator+=(const string&      rhs) {str += rhs.str; return *this;}
-
-#if defined(TOML11_USING_STRING_VIEW) && TOML11_USING_STRING_VIEW>0
-    explicit string(std::string_view s): kind(string_t::basic), str(s){}
-    string(std::string_view s, string_t k): kind(k), str(s){}
-
-    string& operator=(std::string_view s)
-    {kind = string_t::basic; str = s; return *this;}
-
-    explicit operator std::string_view() const noexcept
-    {return std::string_view(str);}
-
-    string& operator+=(const std::string_view& rhs) {str += rhs; return *this;}
-#endif
-
-    string_t    kind;
-    std::string str;
-};
-
-inline bool operator==(const string& lhs, const string& rhs)
-{
-    return lhs.kind == rhs.kind && lhs.str == rhs.str;
-}
-inline bool operator!=(const string& lhs, const string& rhs)
-{
-    return !(lhs == rhs);
-}
-inline bool operator<(const string& lhs, const string& rhs)
-{
-    return (lhs.kind == rhs.kind) ? (lhs.str < rhs.str) : (lhs.kind < rhs.kind);
-}
-inline bool operator>(const string& lhs, const string& rhs)
-{
-    return rhs < lhs;
-}
-inline bool operator<=(const string& lhs, const string& rhs)
-{
-    return !(rhs < lhs);
-}
-inline bool operator>=(const string& lhs, const string& rhs)
-{
-    return !(lhs < rhs);
-}
-
-inline bool
-operator==(const string& lhs, const std::string& rhs) {return lhs.str == rhs;}
-inline bool
-operator!=(const string& lhs, const std::string& rhs) {return lhs.str != rhs;}
-inline bool
-operator< (const string& lhs, const std::string& rhs) {return lhs.str <  rhs;}
-inline bool
-operator> (const string& lhs, const std::string& rhs) {return lhs.str >  rhs;}
-inline bool
-operator<=(const string& lhs, const std::string& rhs) {return lhs.str <= rhs;}
-inline bool
-operator>=(const string& lhs, const std::string& rhs) {return lhs.str >= rhs;}
-
-inline bool
-operator==(const std::string& lhs, const string& rhs) {return lhs == rhs.str;}
-inline bool
-operator!=(const std::string& lhs, const string& rhs) {return lhs != rhs.str;}
-inline bool
-operator< (const std::string& lhs, const string& rhs) {return lhs <  rhs.str;}
-inline bool
-operator> (const std::string& lhs, const string& rhs) {return lhs >  rhs.str;}
-inline bool
-operator<=(const std::string& lhs, const string& rhs) {return lhs <= rhs.str;}
-inline bool
-operator>=(const std::string& lhs, const string& rhs) {return lhs >= rhs.str;}
-
-inline bool
-operator==(const string& lhs, const char* rhs) {return lhs.str == std::string(rhs);}
-inline bool
-operator!=(const string& lhs, const char* rhs) {return lhs.str != std::string(rhs);}
-inline bool
-operator< (const string& lhs, const char* rhs) {return lhs.str <  std::string(rhs);}
-inline bool
-operator> (const string& lhs, const char* rhs) {return lhs.str >  std::string(rhs);}
-inline bool
-operator<=(const string& lhs, const char* rhs) {return lhs.str <= std::string(rhs);}
-inline bool
-operator>=(const string& lhs, const char* rhs) {return lhs.str >= std::string(rhs);}
-
-inline bool
-operator==(const char* lhs, const string& rhs) {return std::string(lhs) == rhs.str;}
-inline bool
-operator!=(const char* lhs, const string& rhs) {return std::string(lhs) != rhs.str;}
-inline bool
-operator< (const char* lhs, const string& rhs) {return std::string(lhs) <  rhs.str;}
-inline bool
-operator> (const char* lhs, const string& rhs) {return std::string(lhs) >  rhs.str;}
-inline bool
-operator<=(const char* lhs, const string& rhs) {return std::string(lhs) <= rhs.str;}
-inline bool
-operator>=(const char* lhs, const string& rhs) {return std::string(lhs) >= rhs.str;}
-
-template<typename charT, typename traits>
-std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, const string& s)
-{
-    if(s.kind == string_t::basic)
-    {
-        if(std::find(s.str.cbegin(), s.str.cend(), '\n') != s.str.cend())
-        {
-            // it contains newline. make it multiline string.
-            os << "\"\"\"\n";
-            for(auto i=s.str.cbegin(), e=s.str.cend(); i!=e; ++i)
-            {
-                switch(*i)
-                {
-                    case '\\': {os << "\\\\"; break;}
-                    case '\"': {os << "\\\""; break;}
-                    case '\b': {os << "\\b";  break;}
-                    case '\t': {os << "\\t";  break;}
-                    case '\f': {os << "\\f";  break;}
-                    case '\n': {os << '\n';   break;}
-                    case '\r':
-                    {
-                        // since it is a multiline string,
-                        // CRLF is not needed to be escaped.
-                        if(std::next(i) != e && *std::next(i) == '\n')
-                        {
-                            os << "\r\n";
-                            ++i;
-                        }
-                        else
-                        {
-                            os << "\\r";
-                        }
-                        break;
-                    }
-                    default: {os << *i; break;}
-                }
-            }
-            os << "\\\n\"\"\"";
-            return os;
-        }
-        // no newline. make it inline.
-        os << "\"";
-        for(const auto c : s.str)
-        {
-            switch(c)
-            {
-                case '\\': {os << "\\\\"; break;}
-                case '\"': {os << "\\\""; break;}
-                case '\b': {os << "\\b";  break;}
-                case '\t': {os << "\\t";  break;}
-                case '\f': {os << "\\f";  break;}
-                case '\n': {os << "\\n";  break;}
-                case '\r': {os << "\\r";  break;}
-                default  : {os << c;      break;}
-            }
-        }
-        os << "\"";
-        return os;
-    }
-    // the string `s` is literal-string.
-    if(std::find(s.str.cbegin(), s.str.cend(), '\n') != s.str.cend() ||
-       std::find(s.str.cbegin(), s.str.cend(), '\'') != s.str.cend() )
-    {
-        // contains newline or single quote. make it multiline.
-        os << "'''\n" << s.str << "'''";
-        return os;
-    }
-    // normal literal string
-    os << '\'' << s.str << '\'';
-    return os;
-}
-
-} // toml
-#endif// TOML11_STRING_H
diff --git a/src/toml11/toml/traits.hpp b/src/toml11/toml/traits.hpp
deleted file mode 100644
index 5495c93b2..000000000
--- a/src/toml11/toml/traits.hpp
+++ /dev/null
@@ -1,327 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_TRAITS_HPP
-#define TOML11_TRAITS_HPP
-
-#include "from.hpp"
-#include "into.hpp"
-
-#include <chrono>
-#include <forward_list>
-#include <string>
-#include <tuple>
-#include <type_traits>
-#include <utility>
-
-#if __cplusplus >= 201703L
-#if __has_include(<string_view>)
-#include <string_view>
-#endif // has_include(<string_view>)
-#endif // cplusplus   >= C++17
-
-namespace toml
-{
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-class basic_value;
-
-namespace detail
-{
-// ---------------------------------------------------------------------------
-// check whether type T is a kind of container/map class
-
-struct has_iterator_impl
-{
-    template<typename T> static std::true_type  check(typename T::iterator*);
-    template<typename T> static std::false_type check(...);
-};
-struct has_value_type_impl
-{
-    template<typename T> static std::true_type  check(typename T::value_type*);
-    template<typename T> static std::false_type check(...);
-};
-struct has_key_type_impl
-{
-    template<typename T> static std::true_type  check(typename T::key_type*);
-    template<typename T> static std::false_type check(...);
-};
-struct has_mapped_type_impl
-{
-    template<typename T> static std::true_type  check(typename T::mapped_type*);
-    template<typename T> static std::false_type check(...);
-};
-struct has_reserve_method_impl
-{
-    template<typename T> static std::false_type check(...);
-    template<typename T> static std::true_type  check(
-        decltype(std::declval<T>().reserve(std::declval<std::size_t>()))*);
-};
-struct has_push_back_method_impl
-{
-    template<typename T> static std::false_type check(...);
-    template<typename T> static std::true_type  check(
-        decltype(std::declval<T>().push_back(std::declval<typename T::value_type>()))*);
-};
-struct is_comparable_impl
-{
-    template<typename T> static std::false_type check(...);
-    template<typename T> static std::true_type  check(
-        decltype(std::declval<T>() < std::declval<T>())*);
-};
-
-struct has_from_toml_method_impl
-{
-    template<typename T, typename C,
-             template<typename ...> class Tb, template<typename ...> class A>
-    static std::true_type  check(
-        decltype(std::declval<T>().from_toml(
-                std::declval<::toml::basic_value<C, Tb, A>>()))*);
-
-    template<typename T, typename C,
-             template<typename ...> class Tb, template<typename ...> class A>
-    static std::false_type check(...);
-};
-struct has_into_toml_method_impl
-{
-    template<typename T>
-    static std::true_type  check(decltype(std::declval<T>().into_toml())*);
-    template<typename T>
-    static std::false_type check(...);
-};
-
-struct has_specialized_from_impl
-{
-    template<typename T>
-    static std::false_type check(...);
-    template<typename T, std::size_t S = sizeof(::toml::from<T>)>
-    static std::true_type check(::toml::from<T>*);
-};
-struct has_specialized_into_impl
-{
-    template<typename T>
-    static std::false_type check(...);
-    template<typename T, std::size_t S = sizeof(::toml::into<T>)>
-    static std::true_type check(::toml::from<T>*);
-};
-
-
-/// Intel C++ compiler can not use decltype in parent class declaration, here
-/// is a hack to work around it. https://stackoverflow.com/a/23953090/4692076
-#ifdef __INTEL_COMPILER
-#define decltype(...) std::enable_if<true, decltype(__VA_ARGS__)>::type
-#endif
-
-template<typename T>
-struct has_iterator    : decltype(has_iterator_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_value_type  : decltype(has_value_type_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_key_type    : decltype(has_key_type_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_mapped_type : decltype(has_mapped_type_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_reserve_method : decltype(has_reserve_method_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_push_back_method : decltype(has_push_back_method_impl::check<T>(nullptr)){};
-template<typename T>
-struct is_comparable : decltype(is_comparable_impl::check<T>(nullptr)){};
-
-template<typename T, typename C,
-         template<typename ...> class Tb, template<typename ...> class A>
-struct has_from_toml_method
-: decltype(has_from_toml_method_impl::check<T, C, Tb, A>(nullptr)){};
-
-template<typename T>
-struct has_into_toml_method
-: decltype(has_into_toml_method_impl::check<T>(nullptr)){};
-
-template<typename T>
-struct has_specialized_from : decltype(has_specialized_from_impl::check<T>(nullptr)){};
-template<typename T>
-struct has_specialized_into : decltype(has_specialized_into_impl::check<T>(nullptr)){};
-
-#ifdef __INTEL_COMPILER
-#undef decltype
-#endif
-
-// ---------------------------------------------------------------------------
-// C++17 and/or/not
-
-#if __cplusplus >= 201703L
-
-using std::conjunction;
-using std::disjunction;
-using std::negation;
-
-#else
-
-template<typename ...> struct conjunction : std::true_type{};
-template<typename T>   struct conjunction<T> : T{};
-template<typename T, typename ... Ts>
-struct conjunction<T, Ts...> :
-    std::conditional<static_cast<bool>(T::value), conjunction<Ts...>, T>::type
-{};
-
-template<typename ...> struct disjunction : std::false_type{};
-template<typename T>   struct disjunction<T> : T {};
-template<typename T, typename ... Ts>
-struct disjunction<T, Ts...> :
-    std::conditional<static_cast<bool>(T::value), T, disjunction<Ts...>>::type
-{};
-
-template<typename T>
-struct negation : std::integral_constant<bool, !static_cast<bool>(T::value)>{};
-
-#endif
-
-// ---------------------------------------------------------------------------
-// type checkers
-
-template<typename T> struct is_std_pair : std::false_type{};
-template<typename T1, typename T2>
-struct is_std_pair<std::pair<T1, T2>> : std::true_type{};
-
-template<typename T> struct is_std_tuple : std::false_type{};
-template<typename ... Ts>
-struct is_std_tuple<std::tuple<Ts...>> : std::true_type{};
-
-template<typename T> struct is_std_forward_list : std::false_type{};
-template<typename T>
-struct is_std_forward_list<std::forward_list<T>> : std::true_type{};
-
-template<typename T> struct is_chrono_duration: std::false_type{};
-template<typename Rep, typename Period>
-struct is_chrono_duration<std::chrono::duration<Rep, Period>>: std::true_type{};
-
-template<typename T>
-struct is_map : conjunction< // map satisfies all the following conditions
-    has_iterator<T>,         // has T::iterator
-    has_value_type<T>,       // has T::value_type
-    has_key_type<T>,         // has T::key_type
-    has_mapped_type<T>       // has T::mapped_type
-    >{};
-template<typename T> struct is_map<T&>                : is_map<T>{};
-template<typename T> struct is_map<T const&>          : is_map<T>{};
-template<typename T> struct is_map<T volatile&>       : is_map<T>{};
-template<typename T> struct is_map<T const volatile&> : is_map<T>{};
-
-template<typename T>
-struct is_container : conjunction<
-    negation<is_map<T>>,                         // not a map
-    negation<std::is_same<T, std::string>>,      // not a std::string
-#if __cplusplus >= 201703L
-#if __has_include(<string_view>)
-    negation<std::is_same<T, std::string_view>>, // not a std::string_view
-#endif // has_include(<string_view>)
-#endif
-    has_iterator<T>,                             // has T::iterator
-    has_value_type<T>                            // has T::value_type
-    >{};
-template<typename T> struct is_container<T&>                : is_container<T>{};
-template<typename T> struct is_container<T const&>          : is_container<T>{};
-template<typename T> struct is_container<T volatile&>       : is_container<T>{};
-template<typename T> struct is_container<T const volatile&> : is_container<T>{};
-
-template<typename T>
-struct is_basic_value: std::false_type{};
-template<typename T> struct is_basic_value<T&>                : is_basic_value<T>{};
-template<typename T> struct is_basic_value<T const&>          : is_basic_value<T>{};
-template<typename T> struct is_basic_value<T volatile&>       : is_basic_value<T>{};
-template<typename T> struct is_basic_value<T const volatile&> : is_basic_value<T>{};
-template<typename C, template<typename ...> class M, template<typename ...> class V>
-struct is_basic_value<::toml::basic_value<C, M, V>>: std::true_type{};
-
-// ---------------------------------------------------------------------------
-// C++14 index_sequence
-
-#if __cplusplus >= 201402L
-
-using std::index_sequence;
-using std::make_index_sequence;
-
-#else
-
-template<std::size_t ... Ns> struct index_sequence{};
-
-template<typename IS, std::size_t N> struct push_back_index_sequence{};
-template<std::size_t N, std::size_t ... Ns>
-struct push_back_index_sequence<index_sequence<Ns...>, N>
-{
-    typedef index_sequence<Ns..., N> type;
-};
-
-template<std::size_t N>
-struct index_sequence_maker
-{
-    typedef typename push_back_index_sequence<
-        typename index_sequence_maker<N-1>::type, N>::type type;
-};
-template<>
-struct index_sequence_maker<0>
-{
-    typedef index_sequence<0> type;
-};
-template<std::size_t N>
-using make_index_sequence = typename index_sequence_maker<N-1>::type;
-
-#endif // __cplusplus >= 2014
-
-// ---------------------------------------------------------------------------
-// C++14 enable_if_t
-
-#if __cplusplus >= 201402L
-
-using std::enable_if_t;
-
-#else
-
-template<bool B, typename T>
-using enable_if_t = typename std::enable_if<B, T>::type;
-
-#endif // __cplusplus >= 2014
-
-// ---------------------------------------------------------------------------
-// return_type_of_t
-
-#if __cplusplus >= 201703L && defined(__cpp_lib_is_invocable) && __cpp_lib_is_invocable>=201703
-
-template<typename F, typename ... Args>
-using return_type_of_t = std::invoke_result_t<F, Args...>;
-
-#else
-// result_of is deprecated after C++17
-template<typename F, typename ... Args>
-using return_type_of_t = typename std::result_of<F(Args...)>::type;
-
-#endif
-
-// ---------------------------------------------------------------------------
-// is_string_literal
-//
-// to use this, pass `typename remove_reference<T>::type` to T.
-
-template<typename T>
-struct is_string_literal:
-disjunction<
-    std::is_same<const char*, T>,
-    conjunction<
-        std::is_array<T>,
-        std::is_same<const char, typename std::remove_extent<T>::type>
-        >
-    >{};
-
-// ---------------------------------------------------------------------------
-// C++20 remove_cvref_t
-
-template<typename T>
-struct remove_cvref
-{
-    using type = typename std::remove_cv<
-        typename std::remove_reference<T>::type>::type;
-};
-
-template<typename T>
-using remove_cvref_t = typename remove_cvref<T>::type;
-
-}// detail
-}//toml
-#endif // TOML_TRAITS
diff --git a/src/toml11/toml/types.hpp b/src/toml11/toml/types.hpp
deleted file mode 100644
index 1e420e7fd..000000000
--- a/src/toml11/toml/types.hpp
+++ /dev/null
@@ -1,173 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_TYPES_HPP
-#define TOML11_TYPES_HPP
-#include <unordered_map>
-#include <vector>
-
-#include "comments.hpp"
-#include "datetime.hpp"
-#include "string.hpp"
-#include "traits.hpp"
-
-namespace toml
-{
-
-template<typename Comment, // discard/preserve_comment
-         template<typename ...> class Table, // map-like class
-         template<typename ...> class Array> // vector-like class
-class basic_value;
-
-using character = char;
-using key = std::string;
-
-#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ <= 4
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Wshadow"
-#endif
-
-using boolean        = bool;
-using integer        = std::int64_t;
-using floating       = double; // "float" is a keyword, cannot use it here.
-// the following stuffs are structs defined here, so aliases are not needed.
-// - string
-// - offset_datetime
-// - offset_datetime
-// - local_datetime
-// - local_date
-// - local_time
-
-#if defined(__GNUC__) && !defined(__clang__)
-#  pragma GCC diagnostic pop
-#endif
-
-// default toml::value and default array/table. these are defined after defining
-// basic_value itself.
-// using value = basic_value<discard_comments, std::unordered_map, std::vector>;
-// using array = typename value::array_type;
-// using table = typename value::table_type;
-
-// to avoid warnings about `value_t::integer` is "shadowing" toml::integer in
-// GCC -Wshadow=global.
-#if defined(__GNUC__) && !defined(__clang__)
-#  pragma GCC diagnostic push
-#  if 7 <= __GNUC__
-#    pragma GCC diagnostic ignored "-Wshadow=global"
-#  else // gcc-6 or older
-#    pragma GCC diagnostic ignored "-Wshadow"
-#  endif
-#endif
-enum class value_t : std::uint8_t
-{
-    empty           =  0,
-    boolean         =  1,
-    integer         =  2,
-    floating        =  3,
-    string          =  4,
-    offset_datetime =  5,
-    local_datetime  =  6,
-    local_date      =  7,
-    local_time      =  8,
-    array           =  9,
-    table           = 10,
-};
-#if defined(__GNUC__) && !defined(__clang__)
-#  pragma GCC diagnostic pop
-#endif
-
-template<typename charT, typename traits>
-inline std::basic_ostream<charT, traits>&
-operator<<(std::basic_ostream<charT, traits>& os, value_t t)
-{
-    switch(t)
-    {
-        case value_t::boolean         : os << "boolean";         return os;
-        case value_t::integer         : os << "integer";         return os;
-        case value_t::floating        : os << "floating";        return os;
-        case value_t::string          : os << "string";          return os;
-        case value_t::offset_datetime : os << "offset_datetime"; return os;
-        case value_t::local_datetime  : os << "local_datetime";  return os;
-        case value_t::local_date      : os << "local_date";      return os;
-        case value_t::local_time      : os << "local_time";      return os;
-        case value_t::array           : os << "array";           return os;
-        case value_t::table           : os << "table";           return os;
-        case value_t::empty           : os << "empty";           return os;
-        default                       : os << "unknown";         return os;
-    }
-}
-
-template<typename charT = char,
-         typename traits = std::char_traits<charT>,
-         typename alloc = std::allocator<charT>>
-inline std::basic_string<charT, traits, alloc> stringize(value_t t)
-{
-    std::basic_ostringstream<charT, traits, alloc> oss;
-    oss << t;
-    return oss.str();
-}
-
-namespace detail
-{
-
-// helper to define a type that represents a value_t value.
-template<value_t V>
-using value_t_constant = std::integral_constant<value_t, V>;
-
-// meta-function that convertes from value_t to the exact toml type that corresponds to.
-// It takes toml::basic_value type because array and table types depend on it.
-template<value_t t, typename Value> struct enum_to_type                      {using type = void                      ;};
-template<typename Value> struct enum_to_type<value_t::empty          , Value>{using type = void                      ;};
-template<typename Value> struct enum_to_type<value_t::boolean        , Value>{using type = boolean                   ;};
-template<typename Value> struct enum_to_type<value_t::integer        , Value>{using type = integer                   ;};
-template<typename Value> struct enum_to_type<value_t::floating       , Value>{using type = floating                  ;};
-template<typename Value> struct enum_to_type<value_t::string         , Value>{using type = string                    ;};
-template<typename Value> struct enum_to_type<value_t::offset_datetime, Value>{using type = offset_datetime           ;};
-template<typename Value> struct enum_to_type<value_t::local_datetime , Value>{using type = local_datetime            ;};
-template<typename Value> struct enum_to_type<value_t::local_date     , Value>{using type = local_date                ;};
-template<typename Value> struct enum_to_type<value_t::local_time     , Value>{using type = local_time                ;};
-template<typename Value> struct enum_to_type<value_t::array          , Value>{using type = typename Value::array_type;};
-template<typename Value> struct enum_to_type<value_t::table          , Value>{using type = typename Value::table_type;};
-
-// meta-function that converts from an exact toml type to the enum that corresponds to.
-template<typename T, typename Value>
-struct type_to_enum : std::conditional<
-    std::is_same<T, typename Value::array_type>::value, // if T == array_type,
-    value_t_constant<value_t::array>,                   // then value_t::array
-    typename std::conditional<                          // else...
-        std::is_same<T, typename Value::table_type>::value, // if T == table_type
-        value_t_constant<value_t::table>,               // then value_t::table
-        value_t_constant<value_t::empty>                // else value_t::empty
-        >::type
-    >::type {};
-template<typename Value> struct type_to_enum<boolean        , Value>: value_t_constant<value_t::boolean        > {};
-template<typename Value> struct type_to_enum<integer        , Value>: value_t_constant<value_t::integer        > {};
-template<typename Value> struct type_to_enum<floating       , Value>: value_t_constant<value_t::floating       > {};
-template<typename Value> struct type_to_enum<string         , Value>: value_t_constant<value_t::string         > {};
-template<typename Value> struct type_to_enum<offset_datetime, Value>: value_t_constant<value_t::offset_datetime> {};
-template<typename Value> struct type_to_enum<local_datetime , Value>: value_t_constant<value_t::local_datetime > {};
-template<typename Value> struct type_to_enum<local_date     , Value>: value_t_constant<value_t::local_date     > {};
-template<typename Value> struct type_to_enum<local_time     , Value>: value_t_constant<value_t::local_time     > {};
-
-// meta-function that checks the type T is the same as one of the toml::* types.
-template<typename T, typename Value>
-struct is_exact_toml_type : disjunction<
-    std::is_same<T, boolean        >,
-    std::is_same<T, integer        >,
-    std::is_same<T, floating       >,
-    std::is_same<T, string         >,
-    std::is_same<T, offset_datetime>,
-    std::is_same<T, local_datetime >,
-    std::is_same<T, local_date     >,
-    std::is_same<T, local_time     >,
-    std::is_same<T, typename Value::array_type>,
-    std::is_same<T, typename Value::table_type>
-    >{};
-template<typename T, typename V> struct is_exact_toml_type<T&, V>               : is_exact_toml_type<T, V>{};
-template<typename T, typename V> struct is_exact_toml_type<T const&, V>         : is_exact_toml_type<T, V>{};
-template<typename T, typename V> struct is_exact_toml_type<T volatile&, V>      : is_exact_toml_type<T, V>{};
-template<typename T, typename V> struct is_exact_toml_type<T const volatile&, V>: is_exact_toml_type<T, V>{};
-
-} // detail
-} // toml
-
-#endif// TOML11_TYPES_H
diff --git a/src/toml11/toml/utility.hpp b/src/toml11/toml/utility.hpp
deleted file mode 100644
index 4a6b4309d..000000000
--- a/src/toml11/toml/utility.hpp
+++ /dev/null
@@ -1,149 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_UTILITY_HPP
-#define TOML11_UTILITY_HPP
-#include <memory>
-#include <sstream>
-#include <utility>
-
-#include "traits.hpp"
-
-#if __cplusplus >= 201402L
-#  define TOML11_MARK_AS_DEPRECATED(msg) [[deprecated(msg)]]
-#elif defined(__GNUC__)
-#  define TOML11_MARK_AS_DEPRECATED(msg) __attribute__((deprecated(msg)))
-#elif defined(_MSC_VER)
-#  define TOML11_MARK_AS_DEPRECATED(msg) __declspec(deprecated(msg))
-#else
-#  define TOML11_MARK_AS_DEPRECATED
-#endif
-
-namespace toml
-{
-
-#if __cplusplus >= 201402L
-
-using std::make_unique;
-
-#else
-
-template<typename T, typename ... Ts>
-inline std::unique_ptr<T> make_unique(Ts&& ... args)
-{
-    return std::unique_ptr<T>(new T(std::forward<Ts>(args)...));
-}
-
-#endif // __cplusplus >= 2014
-
-namespace detail
-{
-template<typename Container>
-void try_reserve_impl(Container& container, std::size_t N, std::true_type)
-{
-    container.reserve(N);
-    return;
-}
-template<typename Container>
-void try_reserve_impl(Container&, std::size_t, std::false_type) noexcept
-{
-    return;
-}
-} // detail
-
-template<typename Container>
-void try_reserve(Container& container, std::size_t N)
-{
-    if(N <= container.size()) {return;}
-    detail::try_reserve_impl(container, N, detail::has_reserve_method<Container>{});
-    return;
-}
-
-namespace detail
-{
-inline std::string concat_to_string_impl(std::ostringstream& oss)
-{
-    return oss.str();
-}
-template<typename T, typename ... Ts>
-std::string concat_to_string_impl(std::ostringstream& oss, T&& head, Ts&& ... tail)
-{
-    oss << std::forward<T>(head);
-    return concat_to_string_impl(oss, std::forward<Ts>(tail) ... );
-}
-} // detail
-
-template<typename ... Ts>
-std::string concat_to_string(Ts&& ... args)
-{
-    std::ostringstream oss;
-    oss << std::boolalpha << std::fixed;
-    return detail::concat_to_string_impl(oss, std::forward<Ts>(args) ...);
-}
-
-template<typename T>
-T from_string(const std::string& str, T opt)
-{
-    T v(opt);
-    std::istringstream iss(str);
-    iss >> v;
-    return v;
-}
-
-namespace detail
-{
-#if __cplusplus >= 201402L
-template<typename T>
-decltype(auto) last_one(T&& tail) noexcept
-{
-    return std::forward<T>(tail);
-}
-
-template<typename T, typename ... Ts>
-decltype(auto) last_one(T&& /*head*/, Ts&& ... tail) noexcept
-{
-    return last_one(std::forward<Ts>(tail)...);
-}
-#else // C++11
-// The following code
-// ```cpp
-//  1 | template<typename T, typename ... Ts>
-//  2 | auto last_one(T&& /*head*/, Ts&& ... tail)
-//  3 |  -> decltype(last_one(std::forward<Ts>(tail)...))
-//  4 | {
-//  5 |     return last_one(std::forward<Ts>(tail)...);
-//  6 | }
-// ```
-// does not work because the function `last_one(...)` is not yet defined at
-// line #3, so `decltype()` cannot deduce the type returned from `last_one`.
-// So we need to determine return type in a different way, like a meta func.
-
-template<typename T, typename ... Ts>
-struct last_one_in_pack
-{
-    using type = typename last_one_in_pack<Ts...>::type;
-};
-template<typename T>
-struct last_one_in_pack<T>
-{
-    using type = T;
-};
-template<typename ... Ts>
-using last_one_in_pack_t = typename last_one_in_pack<Ts...>::type;
-
-template<typename T>
-T&& last_one(T&& tail) noexcept
-{
-    return std::forward<T>(tail);
-}
-template<typename T, typename ... Ts>
-enable_if_t<(sizeof...(Ts) > 0), last_one_in_pack_t<Ts&& ...>>
-last_one(T&& /*head*/, Ts&& ... tail)
-{
-    return last_one(std::forward<Ts>(tail)...);
-}
-
-#endif
-} // detail
-
-}// toml
-#endif // TOML11_UTILITY
diff --git a/src/toml11/toml/value.hpp b/src/toml11/toml/value.hpp
deleted file mode 100644
index 1b43db8d4..000000000
--- a/src/toml11/toml/value.hpp
+++ /dev/null
@@ -1,2035 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_VALUE_HPP
-#define TOML11_VALUE_HPP
-#include <cassert>
-
-#include "comments.hpp"
-#include "exception.hpp"
-#include "into.hpp"
-#include "region.hpp"
-#include "source_location.hpp"
-#include "storage.hpp"
-#include "traits.hpp"
-#include "types.hpp"
-#include "utility.hpp"
-
-namespace toml
-{
-
-namespace detail
-{
-
-// to show error messages. not recommended for users.
-template<typename Value>
-inline region_base const* get_region(const Value& v)
-{
-    return v.region_info_.get();
-}
-
-template<typename Value>
-void change_region(Value& v, region reg)
-{
-    v.region_info_ = std::make_shared<region>(std::move(reg));
-    return;
-}
-
-template<value_t Expected, typename Value>
-[[noreturn]] inline void
-throw_bad_cast(const std::string& funcname, value_t actual, const Value& v)
-{
-    throw type_error(detail::format_underline(
-        concat_to_string(funcname, "bad_cast to ", Expected), {
-            {v.location(), concat_to_string("the actual type is ", actual)}
-        }), v.location());
-}
-
-// Throw `out_of_range` from `toml::value::at()` and `toml::find()`
-// after generating an error message.
-//
-// The implementation is a bit complicated and there are many edge-cases.
-// If you are not interested in the error message generation, just skip this.
-template<typename Value>
-[[noreturn]] void
-throw_key_not_found_error(const Value& v, const key& ky)
-{
-    // The top-level table has its region at the first character of the file.
-    // That means that, in the case when a key is not found in the top-level
-    // table, the error message points to the first character. If the file has
-    // its first table at the first line, the error message would be like this.
-    // ```console
-    // [error] key "a" not found
-    //  --> example.toml
-    //    |
-    //  1 | [table]
-    //    | ^------ in this table
-    // ```
-    // It actually points to the top-level table at the first character,
-    // not `[table]`. But it is too confusing. To avoid the confusion, the error
-    // message should explicitly say "key not found in the top-level table",
-    // or "the parsed file is empty" if there is no content at all (0 bytes in file).
-    const auto loc = v.location();
-    if(loc.line() == 1 && loc.region() == 0)
-    {
-        // First line with a zero-length region means "empty file".
-        // The region will be generated at `parse_toml_file` function
-        // if the file contains no bytes.
-        throw std::out_of_range(format_underline(concat_to_string(
-            "key \"", ky, "\" not found in the top-level table"), {
-                {loc, "the parsed file is empty"}
-            }));
-    }
-    else if(loc.line() == 1 && loc.region() == 1)
-    {
-        // Here it assumes that top-level table starts at the first character.
-        // The region corresponds to the top-level table will be generated at
-        // `parse_toml_file` function.
-        //     It also assumes that the top-level table size is just one and
-        // the line number is `1`. It is always satisfied. And those conditions
-        // are satisfied only if the table is the top-level table.
-        //
-        // 1. one-character dot-key at the first line
-        // ```toml
-        // a.b = "c"
-        // ```
-        // toml11 counts whole key as the table key. Here, `a.b` is the region
-        // of the table "a". It could be counter intuitive, but it works.
-        // The size of the region is 3, not 1. The above example is the shortest
-        // dot-key example. The size cannot be 1.
-        //
-        // 2. one-character inline-table at the first line
-        // ```toml
-        // a = {b = "c"}
-        // ```
-        // toml11 considers the inline table body as the table region. Here,
-        // `{b = "c"}` is the region of the table "a". The size of the region
-        // is 9, not 1. The shotest inline table still has two characters, `{`
-        // and `}`. The size cannot be 1.
-        //
-        // 3. one-character table declaration at the first line
-        // ```toml
-        // [a]
-        // ```
-        // toml11 considers the whole table key as the table region. Here,
-        // `[a]` is the table region. The size is 3, not 1.
-        //
-        throw std::out_of_range(format_underline(concat_to_string(
-            "key \"", ky, "\" not found in the top-level table"), {
-                {loc, "the top-level table starts here"}
-            }));
-    }
-    else
-    {
-        // normal table.
-        throw std::out_of_range(format_underline(concat_to_string(
-            "key \"", ky, "\" not found"), { {loc, "in this table"} }));
-    }
-}
-
-// switch by `value_t` at the compile time.
-template<value_t T>
-struct switch_cast {};
-#define TOML11_GENERATE_SWITCH_CASTER(TYPE) \
-    template<>                                                           \
-    struct switch_cast<value_t::TYPE>                                    \
-    {                                                                    \
-        template<typename Value>                                         \
-        static typename Value::TYPE##_type& invoke(Value& v)             \
-        {                                                                \
-            return v.as_##TYPE();                                        \
-        }                                                                \
-        template<typename Value>                                         \
-        static typename Value::TYPE##_type const& invoke(const Value& v) \
-        {                                                                \
-            return v.as_##TYPE();                                        \
-        }                                                                \
-        template<typename Value>                                         \
-        static typename Value::TYPE##_type&& invoke(Value&& v)           \
-        {                                                                \
-            return std::move(v).as_##TYPE();                             \
-        }                                                                \
-    };                                                                   \
-    /**/
-TOML11_GENERATE_SWITCH_CASTER(boolean)
-TOML11_GENERATE_SWITCH_CASTER(integer)
-TOML11_GENERATE_SWITCH_CASTER(floating)
-TOML11_GENERATE_SWITCH_CASTER(string)
-TOML11_GENERATE_SWITCH_CASTER(offset_datetime)
-TOML11_GENERATE_SWITCH_CASTER(local_datetime)
-TOML11_GENERATE_SWITCH_CASTER(local_date)
-TOML11_GENERATE_SWITCH_CASTER(local_time)
-TOML11_GENERATE_SWITCH_CASTER(array)
-TOML11_GENERATE_SWITCH_CASTER(table)
-
-#undef TOML11_GENERATE_SWITCH_CASTER
-
-}// detail
-
-template<typename Comment, // discard/preserve_comment
-         template<typename ...> class Table = std::unordered_map,
-         template<typename ...> class Array = std::vector>
-class basic_value
-{
-    template<typename T, typename U>
-    static void assigner(T& dst, U&& v)
-    {
-        const auto tmp = ::new(std::addressof(dst)) T(std::forward<U>(v));
-        assert(tmp == std::addressof(dst));
-        (void)tmp;
-    }
-
-    using region_base = detail::region_base;
-
-    template<typename C, template<typename ...> class T,
-             template<typename ...> class A>
-    friend class basic_value;
-
-  public:
-
-    using comment_type         = Comment;
-    using key_type             = ::toml::key;
-    using value_type           = basic_value<comment_type, Table, Array>;
-    using boolean_type         = ::toml::boolean;
-    using integer_type         = ::toml::integer;
-    using floating_type        = ::toml::floating;
-    using string_type          = ::toml::string;
-    using local_time_type      = ::toml::local_time;
-    using local_date_type      = ::toml::local_date;
-    using local_datetime_type  = ::toml::local_datetime;
-    using offset_datetime_type = ::toml::offset_datetime;
-    using array_type           = Array<value_type>;
-    using table_type           = Table<key_type, value_type>;
-
-  public:
-
-    basic_value() noexcept
-        : type_(value_t::empty),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {}
-    ~basic_value() noexcept {this->cleanup();}
-
-    basic_value(const basic_value& v)
-        : type_(v.type()), region_info_(v.region_info_), comments_(v.comments_)
-    {
-        switch(v.type())
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          : assigner(array_          , v.array_          ); break;
-            case value_t::table          : assigner(table_          , v.table_          ); break;
-            default: break;
-        }
-    }
-    basic_value(basic_value&& v)
-        : type_(v.type()), region_info_(std::move(v.region_info_)),
-          comments_(std::move(v.comments_))
-    {
-        switch(this->type_) // here this->type_ is already initialized
-        {
-            case value_t::boolean        : assigner(boolean_        , std::move(v.boolean_        )); break;
-            case value_t::integer        : assigner(integer_        , std::move(v.integer_        )); break;
-            case value_t::floating       : assigner(floating_       , std::move(v.floating_       )); break;
-            case value_t::string         : assigner(string_         , std::move(v.string_         )); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, std::move(v.offset_datetime_)); break;
-            case value_t::local_datetime : assigner(local_datetime_ , std::move(v.local_datetime_ )); break;
-            case value_t::local_date     : assigner(local_date_     , std::move(v.local_date_     )); break;
-            case value_t::local_time     : assigner(local_time_     , std::move(v.local_time_     )); break;
-            case value_t::array          : assigner(array_          , std::move(v.array_          )); break;
-            case value_t::table          : assigner(table_          , std::move(v.table_          )); break;
-            default: break;
-        }
-    }
-    basic_value& operator=(const basic_value& v)
-    {
-        this->cleanup();
-        this->region_info_ = v.region_info_;
-        this->comments_ = v.comments_;
-        this->type_ = v.type();
-        switch(this->type_)
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          : assigner(array_          , v.array_          ); break;
-            case value_t::table          : assigner(table_          , v.table_          ); break;
-            default: break;
-        }
-        return *this;
-    }
-    basic_value& operator=(basic_value&& v)
-    {
-        this->cleanup();
-        this->region_info_ = std::move(v.region_info_);
-        this->comments_ = std::move(v.comments_);
-        this->type_ = v.type();
-        switch(this->type_)
-        {
-            case value_t::boolean        : assigner(boolean_        , std::move(v.boolean_        )); break;
-            case value_t::integer        : assigner(integer_        , std::move(v.integer_        )); break;
-            case value_t::floating       : assigner(floating_       , std::move(v.floating_       )); break;
-            case value_t::string         : assigner(string_         , std::move(v.string_         )); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, std::move(v.offset_datetime_)); break;
-            case value_t::local_datetime : assigner(local_datetime_ , std::move(v.local_datetime_ )); break;
-            case value_t::local_date     : assigner(local_date_     , std::move(v.local_date_     )); break;
-            case value_t::local_time     : assigner(local_time_     , std::move(v.local_time_     )); break;
-            case value_t::array          : assigner(array_          , std::move(v.array_          )); break;
-            case value_t::table          : assigner(table_          , std::move(v.table_          )); break;
-            default: break;
-        }
-        return *this;
-    }
-
-    // overwrite comments ----------------------------------------------------
-
-    basic_value(const basic_value& v, std::vector<std::string> com)
-        : type_(v.type()), region_info_(v.region_info_),
-          comments_(std::move(com))
-    {
-        switch(v.type())
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          : assigner(array_          , v.array_          ); break;
-            case value_t::table          : assigner(table_          , v.table_          ); break;
-            default: break;
-        }
-    }
-
-    basic_value(basic_value&& v, std::vector<std::string> com)
-        : type_(v.type()), region_info_(std::move(v.region_info_)),
-          comments_(std::move(com))
-    {
-        switch(this->type_) // here this->type_ is already initialized
-        {
-            case value_t::boolean        : assigner(boolean_        , std::move(v.boolean_        )); break;
-            case value_t::integer        : assigner(integer_        , std::move(v.integer_        )); break;
-            case value_t::floating       : assigner(floating_       , std::move(v.floating_       )); break;
-            case value_t::string         : assigner(string_         , std::move(v.string_         )); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, std::move(v.offset_datetime_)); break;
-            case value_t::local_datetime : assigner(local_datetime_ , std::move(v.local_datetime_ )); break;
-            case value_t::local_date     : assigner(local_date_     , std::move(v.local_date_     )); break;
-            case value_t::local_time     : assigner(local_time_     , std::move(v.local_time_     )); break;
-            case value_t::array          : assigner(array_          , std::move(v.array_          )); break;
-            case value_t::table          : assigner(table_          , std::move(v.table_          )); break;
-            default: break;
-        }
-    }
-
-    // -----------------------------------------------------------------------
-    // conversion between different basic_values.
-    template<typename C,
-             template<typename ...> class T,
-             template<typename ...> class A>
-    basic_value(const basic_value<C, T, A>& v)
-        : type_(v.type()), region_info_(v.region_info_), comments_(v.comments())
-    {
-        switch(v.type())
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          :
-            {
-                array_type tmp(v.as_array(std::nothrow).begin(),
-                               v.as_array(std::nothrow).end());
-                assigner(array_, std::move(tmp));
-                break;
-            }
-            case value_t::table          :
-            {
-                table_type tmp(v.as_table(std::nothrow).begin(),
-                               v.as_table(std::nothrow).end());
-                assigner(table_, std::move(tmp));
-                break;
-            }
-            default: break;
-        }
-    }
-    template<typename C,
-             template<typename ...> class T,
-             template<typename ...> class A>
-    basic_value(const basic_value<C, T, A>& v, std::vector<std::string> com)
-        : type_(v.type()), region_info_(v.region_info_),
-          comments_(std::move(com))
-    {
-        switch(v.type())
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          :
-            {
-                array_type tmp(v.as_array(std::nothrow).begin(),
-                               v.as_array(std::nothrow).end());
-                assigner(array_, std::move(tmp));
-                break;
-            }
-            case value_t::table          :
-            {
-                table_type tmp(v.as_table(std::nothrow).begin(),
-                               v.as_table(std::nothrow).end());
-                assigner(table_, std::move(tmp));
-                break;
-            }
-            default: break;
-        }
-    }
-    template<typename C,
-             template<typename ...> class T,
-             template<typename ...> class A>
-    basic_value& operator=(const basic_value<C, T, A>& v)
-    {
-        this->region_info_ = v.region_info_;
-        this->comments_    = comment_type(v.comments());
-        this->type_        = v.type();
-        switch(v.type())
-        {
-            case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
-            case value_t::integer        : assigner(integer_        , v.integer_        ); break;
-            case value_t::floating       : assigner(floating_       , v.floating_       ); break;
-            case value_t::string         : assigner(string_         , v.string_         ); break;
-            case value_t::offset_datetime: assigner(offset_datetime_, v.offset_datetime_); break;
-            case value_t::local_datetime : assigner(local_datetime_ , v.local_datetime_ ); break;
-            case value_t::local_date     : assigner(local_date_     , v.local_date_     ); break;
-            case value_t::local_time     : assigner(local_time_     , v.local_time_     ); break;
-            case value_t::array          :
-            {
-                array_type tmp(v.as_array(std::nothrow).begin(),
-                               v.as_array(std::nothrow).end());
-                assigner(array_, std::move(tmp));
-                break;
-            }
-            case value_t::table          :
-            {
-                table_type tmp(v.as_table(std::nothrow).begin(),
-                               v.as_table(std::nothrow).end());
-                assigner(table_, std::move(tmp));
-                break;
-            }
-            default: break;
-        }
-        return *this;
-    }
-
-    // boolean ==============================================================
-
-    basic_value(boolean b)
-        : type_(value_t::boolean),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->boolean_, b);
-    }
-    basic_value& operator=(boolean b)
-    {
-        this->cleanup();
-        this->type_ = value_t::boolean;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->boolean_, b);
-        return *this;
-    }
-    basic_value(boolean b, std::vector<std::string> com)
-        : type_(value_t::boolean),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->boolean_, b);
-    }
-
-    // integer ==============================================================
-
-    template<typename T, typename std::enable_if<detail::conjunction<
-        std::is_integral<T>, detail::negation<std::is_same<T, boolean>>>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value(T i)
-        : type_(value_t::integer),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->integer_, static_cast<integer>(i));
-    }
-
-    template<typename T, typename std::enable_if<detail::conjunction<
-        std::is_integral<T>, detail::negation<std::is_same<T, boolean>>>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value& operator=(T i)
-    {
-        this->cleanup();
-        this->type_ = value_t::integer;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->integer_, static_cast<integer>(i));
-        return *this;
-    }
-
-    template<typename T, typename std::enable_if<detail::conjunction<
-        std::is_integral<T>, detail::negation<std::is_same<T, boolean>>>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value(T i, std::vector<std::string> com)
-        : type_(value_t::integer),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->integer_, static_cast<integer>(i));
-    }
-
-    // floating =============================================================
-
-    template<typename T, typename std::enable_if<
-        std::is_floating_point<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(T f)
-        : type_(value_t::floating),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->floating_, static_cast<floating>(f));
-    }
-
-
-    template<typename T, typename std::enable_if<
-        std::is_floating_point<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value& operator=(T f)
-    {
-        this->cleanup();
-        this->type_ = value_t::floating;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->floating_, static_cast<floating>(f));
-        return *this;
-    }
-
-    template<typename T, typename std::enable_if<
-        std::is_floating_point<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(T f, std::vector<std::string> com)
-        : type_(value_t::floating),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->floating_, f);
-    }
-
-    // string ===============================================================
-
-    basic_value(toml::string s)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, std::move(s));
-    }
-    basic_value& operator=(toml::string s)
-    {
-        this->cleanup();
-        this->type_ = value_t::string ;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->string_, s);
-        return *this;
-    }
-    basic_value(toml::string s, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, std::move(s));
-    }
-
-    basic_value(std::string s)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(std::move(s)));
-    }
-    basic_value& operator=(std::string s)
-    {
-        this->cleanup();
-        this->type_ = value_t::string ;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->string_, toml::string(std::move(s)));
-        return *this;
-    }
-    basic_value(std::string s, string_t kind)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(std::move(s), kind));
-    }
-    basic_value(std::string s, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(std::move(s)));
-    }
-    basic_value(std::string s, string_t kind, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(std::move(s), kind));
-    }
-
-    basic_value(const char* s)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(std::string(s)));
-    }
-    basic_value& operator=(const char* s)
-    {
-        this->cleanup();
-        this->type_ = value_t::string ;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->string_, toml::string(std::string(s)));
-        return *this;
-    }
-    basic_value(const char* s, string_t kind)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(std::string(s), kind));
-    }
-    basic_value(const char* s, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(std::string(s)));
-    }
-    basic_value(const char* s, string_t kind, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(std::string(s), kind));
-    }
-
-#if defined(TOML11_USING_STRING_VIEW) && TOML11_USING_STRING_VIEW>0
-    basic_value(std::string_view s)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(s));
-    }
-    basic_value& operator=(std::string_view s)
-    {
-        this->cleanup();
-        this->type_ = value_t::string ;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->string_, toml::string(s));
-        return *this;
-    }
-    basic_value(std::string_view s, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(s));
-    }
-    basic_value(std::string_view s, string_t kind)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->string_, toml::string(s, kind));
-    }
-    basic_value(std::string_view s, string_t kind, std::vector<std::string> com)
-        : type_(value_t::string),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->string_, toml::string(s, kind));
-    }
-#endif
-
-    // local date ===========================================================
-
-    basic_value(const local_date& ld)
-        : type_(value_t::local_date),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->local_date_, ld);
-    }
-    basic_value& operator=(const local_date& ld)
-    {
-        this->cleanup();
-        this->type_ = value_t::local_date;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->local_date_, ld);
-        return *this;
-    }
-    basic_value(const local_date& ld, std::vector<std::string> com)
-        : type_(value_t::local_date),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->local_date_, ld);
-    }
-
-    // local time ===========================================================
-
-    basic_value(const local_time& lt)
-        : type_(value_t::local_time),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->local_time_, lt);
-    }
-    basic_value(const local_time& lt, std::vector<std::string> com)
-        : type_(value_t::local_time),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->local_time_, lt);
-    }
-    basic_value& operator=(const local_time& lt)
-    {
-        this->cleanup();
-        this->type_ = value_t::local_time;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->local_time_, lt);
-        return *this;
-    }
-
-    template<typename Rep, typename Period>
-    basic_value(const std::chrono::duration<Rep, Period>& dur)
-        : type_(value_t::local_time),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->local_time_, local_time(dur));
-    }
-    template<typename Rep, typename Period>
-    basic_value(const std::chrono::duration<Rep, Period>& dur,
-                std::vector<std::string> com)
-        : type_(value_t::local_time),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->local_time_, local_time(dur));
-    }
-    template<typename Rep, typename Period>
-    basic_value& operator=(const std::chrono::duration<Rep, Period>& dur)
-    {
-        this->cleanup();
-        this->type_ = value_t::local_time;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->local_time_, local_time(dur));
-        return *this;
-    }
-
-    // local datetime =======================================================
-
-    basic_value(const local_datetime& ldt)
-        : type_(value_t::local_datetime),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->local_datetime_, ldt);
-    }
-    basic_value(const local_datetime& ldt, std::vector<std::string> com)
-        : type_(value_t::local_datetime),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->local_datetime_, ldt);
-    }
-    basic_value& operator=(const local_datetime& ldt)
-    {
-        this->cleanup();
-        this->type_ = value_t::local_datetime;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->local_datetime_, ldt);
-        return *this;
-    }
-
-    // offset datetime ======================================================
-
-    basic_value(const offset_datetime& odt)
-        : type_(value_t::offset_datetime),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->offset_datetime_, odt);
-    }
-    basic_value(const offset_datetime& odt, std::vector<std::string> com)
-        : type_(value_t::offset_datetime),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->offset_datetime_, odt);
-    }
-    basic_value& operator=(const offset_datetime& odt)
-    {
-        this->cleanup();
-        this->type_ = value_t::offset_datetime;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->offset_datetime_, odt);
-        return *this;
-    }
-    basic_value(const std::chrono::system_clock::time_point& tp)
-        : type_(value_t::offset_datetime),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->offset_datetime_, offset_datetime(tp));
-    }
-    basic_value(const std::chrono::system_clock::time_point& tp,
-                std::vector<std::string> com)
-        : type_(value_t::offset_datetime),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->offset_datetime_, offset_datetime(tp));
-    }
-    basic_value& operator=(const std::chrono::system_clock::time_point& tp)
-    {
-        this->cleanup();
-        this->type_ = value_t::offset_datetime;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->offset_datetime_, offset_datetime(tp));
-        return *this;
-    }
-
-    // array ================================================================
-
-    basic_value(const array_type& ary)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->array_, ary);
-    }
-    basic_value(const array_type& ary, std::vector<std::string> com)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->array_, ary);
-    }
-    basic_value& operator=(const array_type& ary)
-    {
-        this->cleanup();
-        this->type_ = value_t::array ;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->array_, ary);
-        return *this;
-    }
-
-    // array (initializer_list) ----------------------------------------------
-
-    template<typename T, typename std::enable_if<
-            std::is_convertible<T, value_type>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value(std::initializer_list<T> list)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        array_type ary(list.begin(), list.end());
-        assigner(this->array_, std::move(ary));
-    }
-    template<typename T, typename std::enable_if<
-            std::is_convertible<T, value_type>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value(std::initializer_list<T> list, std::vector<std::string> com)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        array_type ary(list.begin(), list.end());
-        assigner(this->array_, std::move(ary));
-    }
-    template<typename T, typename std::enable_if<
-            std::is_convertible<T, value_type>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value& operator=(std::initializer_list<T> list)
-    {
-        this->cleanup();
-        this->type_ = value_t::array;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-
-        array_type ary(list.begin(), list.end());
-        assigner(this->array_, std::move(ary));
-        return *this;
-    }
-
-    // array (STL Containers) ------------------------------------------------
-
-    template<typename T, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<T, array_type>>,
-            detail::is_container<T>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& list)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        static_assert(std::is_convertible<typename T::value_type, value_type>::value,
-            "elements of a container should be convertible to toml::value");
-
-        array_type ary(list.size());
-        std::copy(list.begin(), list.end(), ary.begin());
-        assigner(this->array_, std::move(ary));
-    }
-    template<typename T, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<T, array_type>>,
-            detail::is_container<T>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& list, std::vector<std::string> com)
-        : type_(value_t::array),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        static_assert(std::is_convertible<typename T::value_type, value_type>::value,
-            "elements of a container should be convertible to toml::value");
-
-        array_type ary(list.size());
-        std::copy(list.begin(), list.end(), ary.begin());
-        assigner(this->array_, std::move(ary));
-    }
-    template<typename T, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<T, array_type>>,
-            detail::is_container<T>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value& operator=(const T& list)
-    {
-        static_assert(std::is_convertible<typename T::value_type, value_type>::value,
-            "elements of a container should be convertible to toml::value");
-
-        this->cleanup();
-        this->type_ = value_t::array;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-
-        array_type ary(list.size());
-        std::copy(list.begin(), list.end(), ary.begin());
-        assigner(this->array_, std::move(ary));
-        return *this;
-    }
-
-    // table ================================================================
-
-    basic_value(const table_type& tab)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        assigner(this->table_, tab);
-    }
-    basic_value(const table_type& tab, std::vector<std::string> com)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        assigner(this->table_, tab);
-    }
-    basic_value& operator=(const table_type& tab)
-    {
-        this->cleanup();
-        this->type_ = value_t::table;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-        assigner(this->table_, tab);
-        return *this;
-    }
-
-    // initializer-list ------------------------------------------------------
-
-    basic_value(std::initializer_list<std::pair<key, basic_value>> list)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        table_type tab;
-        for(const auto& elem : list) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-    }
-
-    basic_value(std::initializer_list<std::pair<key, basic_value>> list,
-                std::vector<std::string> com)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        table_type tab;
-        for(const auto& elem : list) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-    }
-    basic_value& operator=(std::initializer_list<std::pair<key, basic_value>> list)
-    {
-        this->cleanup();
-        this->type_ = value_t::table;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-
-        table_type tab;
-        for(const auto& elem : list) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-        return *this;
-    }
-
-    // other table-like -----------------------------------------------------
-
-    template<typename Map, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<Map, table_type>>,
-            detail::is_map<Map>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const Map& mp)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{}))
-    {
-        table_type tab;
-        for(const auto& elem : mp) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-    }
-    template<typename Map, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<Map, table_type>>,
-            detail::is_map<Map>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const Map& mp, std::vector<std::string> com)
-        : type_(value_t::table),
-          region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(com))
-    {
-        table_type tab;
-        for(const auto& elem : mp) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-    }
-    template<typename Map, typename std::enable_if<detail::conjunction<
-            detail::negation<std::is_same<Map, table_type>>,
-            detail::is_map<Map>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value& operator=(const Map& mp)
-    {
-        this->cleanup();
-        this->type_ = value_t::table;
-        this->region_info_ = std::make_shared<region_base>(region_base{});
-
-        table_type tab;
-        for(const auto& elem : mp) {tab[elem.first] = elem.second;}
-        assigner(this->table_, std::move(tab));
-        return *this;
-    }
-
-    // user-defined =========================================================
-
-    // convert using into_toml() method -------------------------------------
-
-    template<typename T, typename std::enable_if<
-        detail::has_into_toml_method<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& ud): basic_value(ud.into_toml()) {}
-
-    template<typename T, typename std::enable_if<
-        detail::has_into_toml_method<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& ud, std::vector<std::string> com)
-        : basic_value(ud.into_toml(), std::move(com))
-    {}
-    template<typename T, typename std::enable_if<
-        detail::has_into_toml_method<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value& operator=(const T& ud)
-    {
-        *this = ud.into_toml();
-        return *this;
-    }
-
-    // convert using into<T> struct -----------------------------------------
-
-    template<typename T, std::size_t S = sizeof(::toml::into<T>)>
-    basic_value(const T& ud): basic_value(::toml::into<T>::into_toml(ud)) {}
-    template<typename T, std::size_t S = sizeof(::toml::into<T>)>
-    basic_value(const T& ud, std::vector<std::string> com)
-        : basic_value(::toml::into<T>::into_toml(ud), std::move(com))
-    {}
-    template<typename T, std::size_t S = sizeof(::toml::into<T>)>
-    basic_value& operator=(const T& ud)
-    {
-        *this = ::toml::into<T>::into_toml(ud);
-        return *this;
-    }
-
-    // for internal use ------------------------------------------------------
-    //
-    // Those constructors take detail::region that contains parse result.
-
-    basic_value(boolean b, detail::region reg, std::vector<std::string> cm)
-        : type_(value_t::boolean),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->boolean_, b);
-    }
-    template<typename T, typename std::enable_if<
-        detail::conjunction<
-            std::is_integral<T>, detail::negation<std::is_same<T, boolean>>
-        >::value, std::nullptr_t>::type = nullptr>
-    basic_value(T i, detail::region reg, std::vector<std::string> cm)
-        : type_(value_t::integer),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->integer_, static_cast<integer>(i));
-    }
-    template<typename T, typename std::enable_if<
-        std::is_floating_point<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(T f, detail::region reg, std::vector<std::string> cm)
-        : type_(value_t::floating),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->floating_, static_cast<floating>(f));
-    }
-    basic_value(toml::string s, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::string),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->string_, std::move(s));
-    }
-    basic_value(const local_date& ld, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::local_date),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->local_date_, ld);
-    }
-    basic_value(const local_time& lt, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::local_time),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->local_time_, lt);
-    }
-    basic_value(const local_datetime& ldt, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::local_datetime),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->local_datetime_, ldt);
-    }
-    basic_value(const offset_datetime& odt, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::offset_datetime),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->offset_datetime_, odt);
-    }
-    basic_value(const array_type& ary, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::array),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->array_, ary);
-    }
-    basic_value(const table_type& tab, detail::region reg,
-                std::vector<std::string> cm)
-        : type_(value_t::table),
-          region_info_(std::make_shared<detail::region>(std::move(reg))),
-          comments_(std::move(cm))
-    {
-        assigner(this->table_, tab);
-    }
-
-    template<typename T, typename std::enable_if<
-        detail::is_exact_toml_type<T, value_type>::value,
-        std::nullptr_t>::type = nullptr>
-    basic_value(std::pair<T, detail::region> parse_result, std::vector<std::string> com)
-        : basic_value(std::move(parse_result.first),
-                      std::move(parse_result.second),
-                      std::move(com))
-    {}
-
-    // type checking and casting ============================================
-
-    template<typename T, typename std::enable_if<
-        detail::is_exact_toml_type<T, value_type>::value,
-        std::nullptr_t>::type = nullptr>
-    bool is() const noexcept
-    {
-        return detail::type_to_enum<T, value_type>::value == this->type_;
-    }
-    bool is(value_t t) const noexcept {return t == this->type_;}
-
-    bool is_uninitialized()   const noexcept {return this->is(value_t::empty          );}
-    bool is_boolean()         const noexcept {return this->is(value_t::boolean        );}
-    bool is_integer()         const noexcept {return this->is(value_t::integer        );}
-    bool is_floating()        const noexcept {return this->is(value_t::floating       );}
-    bool is_string()          const noexcept {return this->is(value_t::string         );}
-    bool is_offset_datetime() const noexcept {return this->is(value_t::offset_datetime);}
-    bool is_local_datetime()  const noexcept {return this->is(value_t::local_datetime );}
-    bool is_local_date()      const noexcept {return this->is(value_t::local_date     );}
-    bool is_local_time()      const noexcept {return this->is(value_t::local_time     );}
-    bool is_array()           const noexcept {return this->is(value_t::array          );}
-    bool is_table()           const noexcept {return this->is(value_t::table          );}
-
-    value_t type() const noexcept {return type_;}
-
-    template<value_t T>
-    typename detail::enum_to_type<T, value_type>::type&       cast() &
-    {
-        if(this->type_ != T)
-        {
-            detail::throw_bad_cast<T>("toml::value::cast: ", this->type_, *this);
-        }
-        return detail::switch_cast<T>::invoke(*this);
-    }
-    template<value_t T>
-    typename detail::enum_to_type<T, value_type>::type const& cast() const&
-    {
-        if(this->type_ != T)
-        {
-            detail::throw_bad_cast<T>("toml::value::cast: ", this->type_, *this);
-        }
-        return detail::switch_cast<T>::invoke(*this);
-    }
-    template<value_t T>
-    typename detail::enum_to_type<T, value_type>::type&&      cast() &&
-    {
-        if(this->type_ != T)
-        {
-            detail::throw_bad_cast<T>("toml::value::cast: ", this->type_, *this);
-        }
-        return detail::switch_cast<T>::invoke(std::move(*this));
-    }
-
-    // ------------------------------------------------------------------------
-    // nothrow version
-
-    boolean         const& as_boolean        (const std::nothrow_t&) const& noexcept {return this->boolean_;}
-    integer         const& as_integer        (const std::nothrow_t&) const& noexcept {return this->integer_;}
-    floating        const& as_floating       (const std::nothrow_t&) const& noexcept {return this->floating_;}
-    string          const& as_string         (const std::nothrow_t&) const& noexcept {return this->string_;}
-    offset_datetime const& as_offset_datetime(const std::nothrow_t&) const& noexcept {return this->offset_datetime_;}
-    local_datetime  const& as_local_datetime (const std::nothrow_t&) const& noexcept {return this->local_datetime_;}
-    local_date      const& as_local_date     (const std::nothrow_t&) const& noexcept {return this->local_date_;}
-    local_time      const& as_local_time     (const std::nothrow_t&) const& noexcept {return this->local_time_;}
-    array_type      const& as_array          (const std::nothrow_t&) const& noexcept {return this->array_.value();}
-    table_type      const& as_table          (const std::nothrow_t&) const& noexcept {return this->table_.value();}
-
-    boolean        & as_boolean        (const std::nothrow_t&) & noexcept {return this->boolean_;}
-    integer        & as_integer        (const std::nothrow_t&) & noexcept {return this->integer_;}
-    floating       & as_floating       (const std::nothrow_t&) & noexcept {return this->floating_;}
-    string         & as_string         (const std::nothrow_t&) & noexcept {return this->string_;}
-    offset_datetime& as_offset_datetime(const std::nothrow_t&) & noexcept {return this->offset_datetime_;}
-    local_datetime & as_local_datetime (const std::nothrow_t&) & noexcept {return this->local_datetime_;}
-    local_date     & as_local_date     (const std::nothrow_t&) & noexcept {return this->local_date_;}
-    local_time     & as_local_time     (const std::nothrow_t&) & noexcept {return this->local_time_;}
-    array_type     & as_array          (const std::nothrow_t&) & noexcept {return this->array_.value();}
-    table_type     & as_table          (const std::nothrow_t&) & noexcept {return this->table_.value();}
-
-    boolean        && as_boolean        (const std::nothrow_t&) && noexcept {return std::move(this->boolean_);}
-    integer        && as_integer        (const std::nothrow_t&) && noexcept {return std::move(this->integer_);}
-    floating       && as_floating       (const std::nothrow_t&) && noexcept {return std::move(this->floating_);}
-    string         && as_string         (const std::nothrow_t&) && noexcept {return std::move(this->string_);}
-    offset_datetime&& as_offset_datetime(const std::nothrow_t&) && noexcept {return std::move(this->offset_datetime_);}
-    local_datetime && as_local_datetime (const std::nothrow_t&) && noexcept {return std::move(this->local_datetime_);}
-    local_date     && as_local_date     (const std::nothrow_t&) && noexcept {return std::move(this->local_date_);}
-    local_time     && as_local_time     (const std::nothrow_t&) && noexcept {return std::move(this->local_time_);}
-    array_type     && as_array          (const std::nothrow_t&) && noexcept {return std::move(this->array_.value());}
-    table_type     && as_table          (const std::nothrow_t&) && noexcept {return std::move(this->table_.value());}
-
-    // ========================================================================
-    // throw version
-    // ------------------------------------------------------------------------
-    // const reference {{{
-
-    boolean const& as_boolean() const&
-    {
-        if(this->type_ != value_t::boolean)
-        {
-            detail::throw_bad_cast<value_t::boolean>(
-                    "toml::value::as_boolean(): ", this->type_, *this);
-        }
-        return this->boolean_;
-    }
-    integer const& as_integer() const&
-    {
-        if(this->type_ != value_t::integer)
-        {
-            detail::throw_bad_cast<value_t::integer>(
-                    "toml::value::as_integer(): ", this->type_, *this);
-        }
-        return this->integer_;
-    }
-    floating const& as_floating() const&
-    {
-        if(this->type_ != value_t::floating)
-        {
-            detail::throw_bad_cast<value_t::floating>(
-                    "toml::value::as_floating(): ", this->type_, *this);
-        }
-        return this->floating_;
-    }
-    string const& as_string() const&
-    {
-        if(this->type_ != value_t::string)
-        {
-            detail::throw_bad_cast<value_t::string>(
-                    "toml::value::as_string(): ", this->type_, *this);
-        }
-        return this->string_;
-    }
-    offset_datetime const& as_offset_datetime() const&
-    {
-        if(this->type_ != value_t::offset_datetime)
-        {
-            detail::throw_bad_cast<value_t::offset_datetime>(
-                    "toml::value::as_offset_datetime(): ", this->type_, *this);
-        }
-        return this->offset_datetime_;
-    }
-    local_datetime const& as_local_datetime() const&
-    {
-        if(this->type_ != value_t::local_datetime)
-        {
-            detail::throw_bad_cast<value_t::local_datetime>(
-                    "toml::value::as_local_datetime(): ", this->type_, *this);
-        }
-        return this->local_datetime_;
-    }
-    local_date const& as_local_date() const&
-    {
-        if(this->type_ != value_t::local_date)
-        {
-            detail::throw_bad_cast<value_t::local_date>(
-                    "toml::value::as_local_date(): ", this->type_, *this);
-        }
-        return this->local_date_;
-    }
-    local_time const& as_local_time() const&
-    {
-        if(this->type_ != value_t::local_time)
-        {
-            detail::throw_bad_cast<value_t::local_time>(
-                    "toml::value::as_local_time(): ", this->type_, *this);
-        }
-        return this->local_time_;
-    }
-    array_type const& as_array() const&
-    {
-        if(this->type_ != value_t::array)
-        {
-            detail::throw_bad_cast<value_t::array>(
-                    "toml::value::as_array(): ", this->type_, *this);
-        }
-        return this->array_.value();
-    }
-    table_type const& as_table() const&
-    {
-        if(this->type_ != value_t::table)
-        {
-            detail::throw_bad_cast<value_t::table>(
-                    "toml::value::as_table(): ", this->type_, *this);
-        }
-        return this->table_.value();
-    }
-    // }}}
-    // ------------------------------------------------------------------------
-    // nonconst reference {{{
-
-    boolean & as_boolean() &
-    {
-        if(this->type_ != value_t::boolean)
-        {
-            detail::throw_bad_cast<value_t::boolean>(
-                    "toml::value::as_boolean(): ", this->type_, *this);
-        }
-        return this->boolean_;
-    }
-    integer & as_integer() &
-    {
-        if(this->type_ != value_t::integer)
-        {
-            detail::throw_bad_cast<value_t::integer>(
-                    "toml::value::as_integer(): ", this->type_, *this);
-        }
-        return this->integer_;
-    }
-    floating & as_floating() &
-    {
-        if(this->type_ != value_t::floating)
-        {
-            detail::throw_bad_cast<value_t::floating>(
-                    "toml::value::as_floating(): ", this->type_, *this);
-        }
-        return this->floating_;
-    }
-    string & as_string() &
-    {
-        if(this->type_ != value_t::string)
-        {
-            detail::throw_bad_cast<value_t::string>(
-                    "toml::value::as_string(): ", this->type_, *this);
-        }
-        return this->string_;
-    }
-    offset_datetime & as_offset_datetime() &
-    {
-        if(this->type_ != value_t::offset_datetime)
-        {
-            detail::throw_bad_cast<value_t::offset_datetime>(
-                    "toml::value::as_offset_datetime(): ", this->type_, *this);
-        }
-        return this->offset_datetime_;
-    }
-    local_datetime & as_local_datetime() &
-    {
-        if(this->type_ != value_t::local_datetime)
-        {
-            detail::throw_bad_cast<value_t::local_datetime>(
-                    "toml::value::as_local_datetime(): ", this->type_, *this);
-        }
-        return this->local_datetime_;
-    }
-    local_date & as_local_date() &
-    {
-        if(this->type_ != value_t::local_date)
-        {
-            detail::throw_bad_cast<value_t::local_date>(
-                    "toml::value::as_local_date(): ", this->type_, *this);
-        }
-        return this->local_date_;
-    }
-    local_time & as_local_time() &
-    {
-        if(this->type_ != value_t::local_time)
-        {
-            detail::throw_bad_cast<value_t::local_time>(
-                    "toml::value::as_local_time(): ", this->type_, *this);
-        }
-        return this->local_time_;
-    }
-    array_type & as_array() &
-    {
-        if(this->type_ != value_t::array)
-        {
-            detail::throw_bad_cast<value_t::array>(
-                    "toml::value::as_array(): ", this->type_, *this);
-        }
-        return this->array_.value();
-    }
-    table_type & as_table() &
-    {
-        if(this->type_ != value_t::table)
-        {
-            detail::throw_bad_cast<value_t::table>(
-                    "toml::value::as_table(): ", this->type_, *this);
-        }
-        return this->table_.value();
-    }
-
-    // }}}
-    // ------------------------------------------------------------------------
-    // rvalue reference {{{
-
-    boolean && as_boolean() &&
-    {
-        if(this->type_ != value_t::boolean)
-        {
-            detail::throw_bad_cast<value_t::boolean>(
-                    "toml::value::as_boolean(): ", this->type_, *this);
-        }
-        return std::move(this->boolean_);
-    }
-    integer && as_integer() &&
-    {
-        if(this->type_ != value_t::integer)
-        {
-            detail::throw_bad_cast<value_t::integer>(
-                    "toml::value::as_integer(): ", this->type_, *this);
-        }
-        return std::move(this->integer_);
-    }
-    floating && as_floating() &&
-    {
-        if(this->type_ != value_t::floating)
-        {
-            detail::throw_bad_cast<value_t::floating>(
-                    "toml::value::as_floating(): ", this->type_, *this);
-        }
-        return std::move(this->floating_);
-    }
-    string && as_string() &&
-    {
-        if(this->type_ != value_t::string)
-        {
-            detail::throw_bad_cast<value_t::string>(
-                    "toml::value::as_string(): ", this->type_, *this);
-        }
-        return std::move(this->string_);
-    }
-    offset_datetime && as_offset_datetime() &&
-    {
-        if(this->type_ != value_t::offset_datetime)
-        {
-            detail::throw_bad_cast<value_t::offset_datetime>(
-                    "toml::value::as_offset_datetime(): ", this->type_, *this);
-        }
-        return std::move(this->offset_datetime_);
-    }
-    local_datetime && as_local_datetime() &&
-    {
-        if(this->type_ != value_t::local_datetime)
-        {
-            detail::throw_bad_cast<value_t::local_datetime>(
-                    "toml::value::as_local_datetime(): ", this->type_, *this);
-        }
-        return std::move(this->local_datetime_);
-    }
-    local_date && as_local_date() &&
-    {
-        if(this->type_ != value_t::local_date)
-        {
-            detail::throw_bad_cast<value_t::local_date>(
-                    "toml::value::as_local_date(): ", this->type_, *this);
-        }
-        return std::move(this->local_date_);
-    }
-    local_time && as_local_time() &&
-    {
-        if(this->type_ != value_t::local_time)
-        {
-            detail::throw_bad_cast<value_t::local_time>(
-                    "toml::value::as_local_time(): ", this->type_, *this);
-        }
-        return std::move(this->local_time_);
-    }
-    array_type && as_array() &&
-    {
-        if(this->type_ != value_t::array)
-        {
-            detail::throw_bad_cast<value_t::array>(
-                    "toml::value::as_array(): ", this->type_, *this);
-        }
-        return std::move(this->array_.value());
-    }
-    table_type && as_table() &&
-    {
-        if(this->type_ != value_t::table)
-        {
-            detail::throw_bad_cast<value_t::table>(
-                    "toml::value::as_table(): ", this->type_, *this);
-        }
-        return std::move(this->table_.value());
-    }
-    // }}}
-
-    // accessors =============================================================
-    //
-    // may throw type_error or out_of_range
-    //
-    value_type&       at(const key& k)
-    {
-        if(!this->is_table())
-        {
-            detail::throw_bad_cast<value_t::table>(
-                "toml::value::at(key): ", this->type_, *this);
-        }
-        if(this->as_table(std::nothrow).count(k) == 0)
-        {
-            detail::throw_key_not_found_error(*this, k);
-        }
-        return this->as_table(std::nothrow).at(k);
-    }
-    value_type const& at(const key& k) const
-    {
-        if(!this->is_table())
-        {
-            detail::throw_bad_cast<value_t::table>(
-                "toml::value::at(key): ", this->type_, *this);
-        }
-        if(this->as_table(std::nothrow).count(k) == 0)
-        {
-            detail::throw_key_not_found_error(*this, k);
-        }
-        return this->as_table(std::nothrow).at(k);
-    }
-    value_type&       operator[](const key& k)
-    {
-        if(this->is_uninitialized())
-        {
-            *this = table_type{};
-        }
-        else if(!this->is_table()) // initialized, but not a table
-        {
-            detail::throw_bad_cast<value_t::table>(
-                "toml::value::operator[](key): ", this->type_, *this);
-        }
-        return this->as_table(std::nothrow)[k];
-    }
-
-    value_type&       at(const std::size_t idx)
-    {
-        if(!this->is_array())
-        {
-            detail::throw_bad_cast<value_t::array>(
-                "toml::value::at(idx): ", this->type_, *this);
-        }
-        if(this->as_array(std::nothrow).size() <= idx)
-        {
-            throw std::out_of_range(detail::format_underline(
-                "toml::value::at(idx): no element corresponding to the index", {
-                    {this->location(), concat_to_string("the length is ",
-                        this->as_array(std::nothrow).size(),
-                        ", and the specified index is ", idx)}
-                }));
-        }
-        return this->as_array().at(idx);
-    }
-    value_type const& at(const std::size_t idx) const
-    {
-        if(!this->is_array())
-        {
-            detail::throw_bad_cast<value_t::array>(
-                "toml::value::at(idx): ", this->type_, *this);
-        }
-        if(this->as_array(std::nothrow).size() <= idx)
-        {
-            throw std::out_of_range(detail::format_underline(
-                "toml::value::at(idx): no element corresponding to the index", {
-                    {this->location(), concat_to_string("the length is ",
-                        this->as_array(std::nothrow).size(),
-                        ", and the specified index is ", idx)}
-                }));
-        }
-        return this->as_array(std::nothrow).at(idx);
-    }
-
-    value_type&       operator[](const std::size_t idx) noexcept
-    {
-        // no check...
-        return this->as_array(std::nothrow)[idx];
-    }
-    value_type const& operator[](const std::size_t idx) const noexcept
-    {
-        // no check...
-        return this->as_array(std::nothrow)[idx];
-    }
-
-    void push_back(const value_type& x)
-    {
-        if(!this->is_array())
-        {
-            detail::throw_bad_cast<value_t::array>(
-                "toml::value::push_back(value): ", this->type_, *this);
-        }
-        this->as_array(std::nothrow).push_back(x);
-        return;
-    }
-    void push_back(value_type&& x)
-    {
-        if(!this->is_array())
-        {
-            detail::throw_bad_cast<value_t::array>(
-                "toml::value::push_back(value): ", this->type_, *this);
-        }
-        this->as_array(std::nothrow).push_back(std::move(x));
-        return;
-    }
-
-    template<typename ... Ts>
-    value_type& emplace_back(Ts&& ... args)
-    {
-        if(!this->is_array())
-        {
-            detail::throw_bad_cast<value_t::array>(
-                "toml::value::emplace_back(...): ", this->type_, *this);
-        }
-        this->as_array(std::nothrow).emplace_back(std::forward<Ts>(args) ...);
-        return this->as_array(std::nothrow).back();
-    }
-
-    std::size_t size() const
-    {
-        switch(this->type_)
-        {
-            case value_t::array:
-            {
-                return this->as_array(std::nothrow).size();
-            }
-            case value_t::table:
-            {
-                return this->as_table(std::nothrow).size();
-            }
-            case value_t::string:
-            {
-                return this->as_string(std::nothrow).str.size();
-            }
-            default:
-            {
-                throw type_error(detail::format_underline(
-                    "toml::value::size(): bad_cast to container types", {
-                        {this->location(),
-                         concat_to_string("the actual type is ", this->type_)}
-                    }), this->location());
-            }
-        }
-    }
-
-    std::size_t count(const key_type& k) const
-    {
-        if(!this->is_table())
-        {
-            detail::throw_bad_cast<value_t::table>(
-                "toml::value::count(key): ", this->type_, *this);
-        }
-        return this->as_table(std::nothrow).count(k);
-    }
-
-    bool contains(const key_type& k) const
-    {
-        if(!this->is_table())
-        {
-            detail::throw_bad_cast<value_t::table>(
-                "toml::value::contains(key): ", this->type_, *this);
-        }
-        return (this->as_table(std::nothrow).count(k) != 0);
-    }
-
-    source_location location() const
-    {
-        return source_location(this->region_info_.get());
-    }
-
-    comment_type const& comments() const noexcept {return this->comments_;}
-    comment_type&       comments()       noexcept {return this->comments_;}
-
-  private:
-
-    void cleanup() noexcept
-    {
-        switch(this->type_)
-        {
-            case value_t::string  : {string_.~string();       return;}
-            case value_t::array   : {array_.~array_storage(); return;}
-            case value_t::table   : {table_.~table_storage(); return;}
-            default              : return;
-        }
-    }
-
-    // for error messages
-    template<typename Value>
-    friend region_base const* detail::get_region(const Value& v);
-
-    template<typename Value>
-    friend void detail::change_region(Value& v, detail::region reg);
-
-  private:
-
-    using array_storage = detail::storage<array_type>;
-    using table_storage = detail::storage<table_type>;
-
-    value_t type_;
-    union
-    {
-        boolean         boolean_;
-        integer         integer_;
-        floating        floating_;
-        string          string_;
-        offset_datetime offset_datetime_;
-        local_datetime  local_datetime_;
-        local_date      local_date_;
-        local_time      local_time_;
-        array_storage   array_;
-        table_storage   table_;
-    };
-    std::shared_ptr<region_base> region_info_;
-    comment_type                 comments_;
-};
-
-// default toml::value and default array/table.
-// TOML11_DEFAULT_COMMENT_STRATEGY is defined in comments.hpp
-using value = basic_value<TOML11_DEFAULT_COMMENT_STRATEGY, std::unordered_map, std::vector>;
-using array = typename value::array_type;
-using table = typename value::table_type;
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-inline bool
-operator==(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    if(lhs.type()     != rhs.type())     {return false;}
-    if(lhs.comments() != rhs.comments()) {return false;}
-
-    switch(lhs.type())
-    {
-        case value_t::boolean  :
-        {
-            return lhs.as_boolean() == rhs.as_boolean();
-        }
-        case value_t::integer  :
-        {
-            return lhs.as_integer() == rhs.as_integer();
-        }
-        case value_t::floating :
-        {
-            return lhs.as_floating() == rhs.as_floating();
-        }
-        case value_t::string   :
-        {
-            return lhs.as_string() == rhs.as_string();
-        }
-        case value_t::offset_datetime:
-        {
-            return lhs.as_offset_datetime() == rhs.as_offset_datetime();
-        }
-        case value_t::local_datetime:
-        {
-            return lhs.as_local_datetime() == rhs.as_local_datetime();
-        }
-        case value_t::local_date:
-        {
-            return lhs.as_local_date() == rhs.as_local_date();
-        }
-        case value_t::local_time:
-        {
-            return lhs.as_local_time() == rhs.as_local_time();
-        }
-        case value_t::array    :
-        {
-            return lhs.as_array() == rhs.as_array();
-        }
-        case value_t::table    :
-        {
-            return lhs.as_table() == rhs.as_table();
-        }
-        case value_t::empty    : {return true; }
-        default:                 {return false;}
-    }
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-inline bool operator!=(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    return !(lhs == rhs);
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-typename std::enable_if<detail::conjunction<
-    detail::is_comparable<typename basic_value<C, T, A>::array_type>,
-    detail::is_comparable<typename basic_value<C, T, A>::table_type>
-    >::value, bool>::type
-operator<(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    if(lhs.type() != rhs.type()){return (lhs.type() < rhs.type());}
-    switch(lhs.type())
-    {
-        case value_t::boolean  :
-        {
-            return lhs.as_boolean() <  rhs.as_boolean() ||
-                  (lhs.as_boolean() == rhs.as_boolean() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::integer  :
-        {
-            return lhs.as_integer() <  rhs.as_integer() ||
-                  (lhs.as_integer() == rhs.as_integer() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::floating :
-        {
-            return lhs.as_floating() <  rhs.as_floating() ||
-                  (lhs.as_floating() == rhs.as_floating() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::string   :
-        {
-            return lhs.as_string() <  rhs.as_string() ||
-                  (lhs.as_string() == rhs.as_string() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::offset_datetime:
-        {
-            return lhs.as_offset_datetime() <  rhs.as_offset_datetime() ||
-                  (lhs.as_offset_datetime() == rhs.as_offset_datetime() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::local_datetime:
-        {
-            return lhs.as_local_datetime() <  rhs.as_local_datetime() ||
-                  (lhs.as_local_datetime() == rhs.as_local_datetime() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::local_date:
-        {
-            return lhs.as_local_date() <  rhs.as_local_date() ||
-                  (lhs.as_local_date() == rhs.as_local_date() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::local_time:
-        {
-            return lhs.as_local_time() <  rhs.as_local_time() ||
-                  (lhs.as_local_time() == rhs.as_local_time() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::array    :
-        {
-            return lhs.as_array() <  rhs.as_array() ||
-                  (lhs.as_array() == rhs.as_array() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::table    :
-        {
-            return lhs.as_table() <  rhs.as_table() ||
-                  (lhs.as_table() == rhs.as_table() &&
-                   lhs.comments() < rhs.comments());
-        }
-        case value_t::empty    :
-        {
-            return lhs.comments() < rhs.comments();
-        }
-        default:
-        {
-            return lhs.comments() < rhs.comments();
-        }
-    }
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-typename std::enable_if<detail::conjunction<
-    detail::is_comparable<typename basic_value<C, T, A>::array_type>,
-    detail::is_comparable<typename basic_value<C, T, A>::table_type>
-    >::value, bool>::type
-operator<=(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    return (lhs < rhs) || (lhs == rhs);
-}
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-typename std::enable_if<detail::conjunction<
-    detail::is_comparable<typename basic_value<C, T, A>::array_type>,
-    detail::is_comparable<typename basic_value<C, T, A>::table_type>
-    >::value, bool>::type
-operator>(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    return !(lhs <= rhs);
-}
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-typename std::enable_if<detail::conjunction<
-    detail::is_comparable<typename basic_value<C, T, A>::array_type>,
-    detail::is_comparable<typename basic_value<C, T, A>::table_type>
-    >::value, bool>::type
-operator>=(const basic_value<C, T, A>& lhs, const basic_value<C, T, A>& rhs)
-{
-    return !(lhs < rhs);
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-inline std::string format_error(const std::string& err_msg,
-        const basic_value<C, T, A>& v, const std::string& comment,
-        std::vector<std::string> hints = {},
-        const bool colorize = TOML11_ERROR_MESSAGE_COLORIZED)
-{
-    return detail::format_underline(err_msg, {{v.location(), comment}},
-                                    std::move(hints), colorize);
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-inline std::string format_error(const std::string& err_msg,
-        const toml::basic_value<C, T, A>& v1, const std::string& comment1,
-        const toml::basic_value<C, T, A>& v2, const std::string& comment2,
-        std::vector<std::string> hints = {},
-        const bool colorize = TOML11_ERROR_MESSAGE_COLORIZED)
-{
-    return detail::format_underline(err_msg, {
-            {v1.location(), comment1}, {v2.location(), comment2}
-        }, std::move(hints), colorize);
-}
-
-template<typename C, template<typename ...> class T, template<typename ...> class A>
-inline std::string format_error(const std::string& err_msg,
-        const toml::basic_value<C, T, A>& v1, const std::string& comment1,
-        const toml::basic_value<C, T, A>& v2, const std::string& comment2,
-        const toml::basic_value<C, T, A>& v3, const std::string& comment3,
-        std::vector<std::string> hints = {},
-        const bool colorize = TOML11_ERROR_MESSAGE_COLORIZED)
-{
-    return detail::format_underline(err_msg, {{v1.location(), comment1},
-            {v2.location(), comment2}, {v3.location(), comment3}
-        }, std::move(hints), colorize);
-}
-
-template<typename Visitor, typename C,
-         template<typename ...> class T, template<typename ...> class A>
-detail::return_type_of_t<Visitor, const toml::boolean&>
-visit(Visitor&& visitor, const toml::basic_value<C, T, A>& v)
-{
-    switch(v.type())
-    {
-        case value_t::boolean        : {return visitor(v.as_boolean        ());}
-        case value_t::integer        : {return visitor(v.as_integer        ());}
-        case value_t::floating       : {return visitor(v.as_floating       ());}
-        case value_t::string         : {return visitor(v.as_string         ());}
-        case value_t::offset_datetime: {return visitor(v.as_offset_datetime());}
-        case value_t::local_datetime : {return visitor(v.as_local_datetime ());}
-        case value_t::local_date     : {return visitor(v.as_local_date     ());}
-        case value_t::local_time     : {return visitor(v.as_local_time     ());}
-        case value_t::array          : {return visitor(v.as_array          ());}
-        case value_t::table          : {return visitor(v.as_table          ());}
-        case value_t::empty          : break;
-        default: break;
-    }
-    throw std::runtime_error(format_error("[error] toml::visit: toml::basic_value "
-            "does not have any valid basic_value.", v, "here"));
-}
-
-template<typename Visitor, typename C,
-         template<typename ...> class T, template<typename ...> class A>
-detail::return_type_of_t<Visitor, toml::boolean&>
-visit(Visitor&& visitor, toml::basic_value<C, T, A>& v)
-{
-    switch(v.type())
-    {
-        case value_t::boolean        : {return visitor(v.as_boolean        ());}
-        case value_t::integer        : {return visitor(v.as_integer        ());}
-        case value_t::floating       : {return visitor(v.as_floating       ());}
-        case value_t::string         : {return visitor(v.as_string         ());}
-        case value_t::offset_datetime: {return visitor(v.as_offset_datetime());}
-        case value_t::local_datetime : {return visitor(v.as_local_datetime ());}
-        case value_t::local_date     : {return visitor(v.as_local_date     ());}
-        case value_t::local_time     : {return visitor(v.as_local_time     ());}
-        case value_t::array          : {return visitor(v.as_array          ());}
-        case value_t::table          : {return visitor(v.as_table          ());}
-        case value_t::empty          : break;
-        default: break;
-    }
-    throw std::runtime_error(format_error("[error] toml::visit: toml::basic_value "
-            "does not have any valid basic_value.", v, "here"));
-}
-
-template<typename Visitor, typename C,
-         template<typename ...> class T, template<typename ...> class A>
-detail::return_type_of_t<Visitor, toml::boolean&&>
-visit(Visitor&& visitor, toml::basic_value<C, T, A>&& v)
-{
-    switch(v.type())
-    {
-        case value_t::boolean        : {return visitor(std::move(v.as_boolean        ()));}
-        case value_t::integer        : {return visitor(std::move(v.as_integer        ()));}
-        case value_t::floating       : {return visitor(std::move(v.as_floating       ()));}
-        case value_t::string         : {return visitor(std::move(v.as_string         ()));}
-        case value_t::offset_datetime: {return visitor(std::move(v.as_offset_datetime()));}
-        case value_t::local_datetime : {return visitor(std::move(v.as_local_datetime ()));}
-        case value_t::local_date     : {return visitor(std::move(v.as_local_date     ()));}
-        case value_t::local_time     : {return visitor(std::move(v.as_local_time     ()));}
-        case value_t::array          : {return visitor(std::move(v.as_array          ()));}
-        case value_t::table          : {return visitor(std::move(v.as_table          ()));}
-        case value_t::empty          : break;
-        default: break;
-    }
-    throw std::runtime_error(format_error("[error] toml::visit: toml::basic_value "
-            "does not have any valid basic_value.", v, "here"));
-}
-
-}// toml
-#endif// TOML11_VALUE