lix/src/libexpr/symbol-table.hh
Eelco Dolstra 0b305c534f * Store attribute sets as a vector instead of a map (i.e. a red-black
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).
2010-10-24 00:41:29 +00:00

93 lines
1.7 KiB
C++

#ifndef __SYMBOL_TABLE_H
#define __SYMBOL_TABLE_H
#include "config.h"
#include <map>
#if HAVE_TR1_UNORDERED_SET
#include <tr1/unordered_set>
#endif
#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:
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 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:
#if HAVE_TR1_UNORDERED_SET
typedef std::tr1::unordered_set<string> Symbols;
#else
typedef std::set<string> Symbols;
#endif
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 */