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#pragma once
#include <absl/container/node_hash_set.h>
#include <absl/strings/string_view.h>
#include "types.hh"
namespace nix { // TODO(tazjin): ::expr
/* 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; }
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; }
bool set() const { return s; }
bool empty() const { return s->empty(); }
friend std::ostream& operator<<(std::ostream& str, const Symbol& sym);
};
class SymbolTable {
public:
Symbol Create(absl::string_view sym);
// TODO(tazjin): two of these?
size_t Size() const;
// Return the total size (in bytes)
size_t TotalSize() const;
private:
// flat_hash_set does not retain pointer stability on rehashing,
// hence "interned" strings/symbols are stored on the heap.
absl::node_hash_set<std::string> symbols_;
};
} // namespace nix
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