path: root/third_party/nix/src/libexpr/symbol-table.hh

#pragma once

#include <map>
#include <unordered_set>
#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 string* s;  // pointer into SymbolTable
  Symbol(const string* s) : s(s){};
  friend class SymbolTable;

 public:
  Symbol() : s(0){};

  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 set() const { return s; }

  bool empty() const { return s->empty(); }

  friend std::ostream& operator<<(std::ostream& str, const Symbol& sym);
};

class SymbolTable {
 private:
  typedef std::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);
  }

  size_t size() const { return symbols.size(); }

  size_t totalSize() const;

  template <typename T>
  void dump(T callback) {
    for (auto& s : symbols) callback(s);
  }
};

}  // namespace nix