#ifndef __SYMBOL_TABLE_H #define __SYMBOL_TABLE_H #include <map> #include <tr1/unordered_set> #include "types.hh" namespace nix { /* Symbol table used by the parser and evaluator to represent and look up identifiers and attribute sets 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 string * s; // pointer into SymbolTable Symbol(const string * s) : s(s) { }; friend class SymbolTable; public: bool operator == (const Symbol & s2) const { return s == s2.s; } bool operator != (const Symbol & s2) const { return s != s2.s; } bool operator < (const Symbol & s2) const { return s < s2.s; } operator const string & () const { return *s; } bool empty() const { return s->empty(); } friend std::ostream & operator << (std::ostream & str, const Symbol & sym); }; inline std::ostream & operator << (std::ostream & str, const Symbol & sym) { str << *sym.s; return str; } class SymbolTable { private: typedef std::tr1::unordered_set<string> Symbols; Symbols symbols; public: Symbol create(const string & s) { std::pair<Symbols::iterator, bool> res = symbols.insert(s); return Symbol(&*res.first); } unsigned int size() const { return symbols.size(); } }; } #endif /* !__SYMBOL_TABLE_H */