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#pragma once
#include <list>
#include <map>
#include <unordered_map>
#include "types.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 a pointer equality test),
because the symbol table stores only one copy of each string. */
class Symbol
{
private:
const std::string * s; // pointer into SymbolTable
Symbol(const std::string * s) : s(s) { };
friend class SymbolTable;
public:
Symbol() : s(0) { };
bool operator == (const Symbol & s2) const
{
return s == s2.s;
}
// FIXME: remove
bool operator == (std::string_view s2) const
{
return s->compare(s2) == 0;
}
bool operator != (const Symbol & s2) const
{
return s != s2.s;
}
bool operator < (const Symbol & s2) const
{
return s < s2.s;
}
operator const std::string & () const
{
return *s;
}
operator const std::string_view () const
{
return *s;
}
bool set() const
{
return s;
}
bool empty() const
{
return s->empty();
}
friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
};
class SymbolTable
{
private:
std::unordered_map<std::string_view, Symbol> symbols;
std::list<std::string> store;
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
auto it = symbols.find(s);
if (it != symbols.end()) return it->second;
auto & rawSym = store.emplace_back(s);
return symbols.emplace(rawSym, Symbol(&rawSym)).first->second;
}
size_t size() const
{
return symbols.size();
}
size_t totalSize() const;
template<typename T>
void dump(T callback)
{
for (auto & s : store)
callback(s);
}
};
}
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