90 lines
1.7 KiB
C++
90 lines
1.7 KiB
C++
#pragma once
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#include "config.h"
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#include <map>
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#if HAVE_TR1_UNORDERED_SET
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#include <tr1/unordered_set>
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#endif
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#include "types.hh"
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namespace nix {
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/* Symbol table used by the parser and evaluator to represent and look
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up identifiers and attribute sets efficiently.
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SymbolTable::create() converts a string into a symbol. Symbols
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have the property that they can be compared efficiently (using a
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pointer equality test), because the symbol table stores only one
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copy of each string. */
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class Symbol
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{
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private:
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const string * s; // pointer into SymbolTable
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Symbol(const string * s) : s(s) { };
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friend class SymbolTable;
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public:
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Symbol() : s(0) { };
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bool operator == (const Symbol & s2) const
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{
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return s == s2.s;
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}
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bool operator != (const Symbol & s2) const
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{
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return s != s2.s;
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}
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bool operator < (const Symbol & s2) const
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{
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return s < s2.s;
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}
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operator const string & () const
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{
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return *s;
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}
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bool empty() const
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{
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return s->empty();
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}
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friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
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};
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inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
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{
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str << *sym.s;
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return str;
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}
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class SymbolTable
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{
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private:
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#if HAVE_TR1_UNORDERED_SET
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typedef std::tr1::unordered_set<string> Symbols;
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#else
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typedef std::set<string> Symbols;
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#endif
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Symbols symbols;
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public:
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Symbol create(const string & s)
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{
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std::pair<Symbols::iterator, bool> res = symbols.insert(s);
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return Symbol(&*res.first);
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}
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unsigned int size() const
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{
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return symbols.size();
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}
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};
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}
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