forked from lix-project/lix
0b305c534f
tree). This saves a lot of memory. The vector should be sorted so
that names can be looked up using binary search, but this is not the
case yet. (Surprisingly, looking up attributes using linear search
doesn't have a big impact on performance.)
Memory consumption for
$ nix-instantiate /etc/nixos/nixos/tests -A bittorrent.test --readonly-mode
on x86_64-linux with GC enabled is now 185 MiB (compared to 946
MiB on the trunk).
93 lines
1.7 KiB
C++
93 lines
1.7 KiB
C++
#ifndef __SYMBOL_TABLE_H
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#define __SYMBOL_TABLE_H
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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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#endif /* !__SYMBOL_TABLE_H */
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