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#pragma once
///@file
#include <list>
#include <map>
#include <unordered_map>
#include "types.hh"
#include "chunked-vector.hh"
namespace nix {
/* Symbol table used by the parser and evaluator to represent and look
up identifiers and attributes efficiently. SymbolTable::create()
converts a string into a symbol. Symbols have the property that
they can be compared efficiently (using an equality test),
because the symbol table stores only one copy of each string. */
/* This class mainly exists to give us an operator<< for ostreams. We could also
return plain strings from SymbolTable, but then we'd have to wrap every
instance of a symbol that is fmt()ed, which is inconvenient and error-prone. */
class SymbolStr
{
friend class SymbolTable;
private:
const std::string * s;
explicit SymbolStr(const std::string & symbol): s(&symbol) {}
public:
bool operator == (std::string_view s2) const
{
return *s == s2;
}
operator const std::string & () const
{
return *s;
}
operator const std::string_view () const
{
return *s;
}
friend std::ostream & operator <<(std::ostream & os, const SymbolStr & symbol);
};
class Symbol
{
friend class SymbolTable;
private:
uint32_t id;
explicit Symbol(uint32_t id): id(id) {}
public:
Symbol() : id(0) {}
explicit operator bool() const { return id > 0; }
bool operator<(const Symbol other) const { return id < other.id; }
bool operator==(const Symbol other) const { return id == other.id; }
bool operator!=(const Symbol other) const { return id != other.id; }
};
class SymbolTable
{
private:
std::unordered_map<std::string_view, std::pair<const std::string *, uint32_t>> symbols;
ChunkedVector<std::string, 8192> store{16};
public:
Symbol create(std::string_view s)
{
// Most symbols are looked up more than once, so we trade off insertion performance
// for lookup performance.
// TODO: could probably be done more efficiently with transparent Hash and Equals
// on the original implementation using unordered_set
// FIXME: make this thread-safe.
auto it = symbols.find(s);
if (it != symbols.end()) return Symbol(it->second.second + 1);
const auto & [rawSym, idx] = store.add(std::string(s));
symbols.emplace(rawSym, std::make_pair(&rawSym, idx));
return Symbol(idx + 1);
}
std::vector<SymbolStr> resolve(const std::vector<Symbol> & symbols) const
{
std::vector<SymbolStr> result;
result.reserve(symbols.size());
for (auto sym : symbols)
result.push_back((*this)[sym]);
return result;
}
SymbolStr operator[](Symbol s) const
{
if (s.id == 0 || s.id > store.size())
abort();
return SymbolStr(store[s.id - 1]);
}
size_t size() const
{
return store.size();
}
size_t totalSize() const;
template<typename T>
void dump(T callback) const
{
store.forEach(callback);
}
};
}
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