ifndef SymbolAsString
sclass symbol_Tester {
  Symbol symbol;
  
  *() {}
  *(Symbol *symbol) {}
  
  public int hashCode() { ret symbol.text.hashCode(); }
  public bool equals(O o) {
    if (!o instanceof symbol_Tester) false;
    ret eq(symbol.text, o/symbol_Tester.symbol.text);
  }
}

static WeakHashMap<symbol_Tester, Bool> symbol_map = unsyncedWeakHashMap();
static WeakHashMap<MasterSymbol, Bool> masterSymbol_map = unsyncedWeakHashMap();
endifndef

static Symbol symbol(S s) {
  ifdef SymbolAsString
  ret s;
  endifdef
  ifndef SymbolAsString
  if (s == null) null;
  synchronized(symbol_map) {
    // This is a trick that works because of how WeakHashMap compares keys.
    symbol_Tester tester = symbol_Tester(new MasterSymbol(s, true));
    O e = call(symbol_map, 'getEntry, tester);
    symbol_Tester sym = e == null ? null : ((WeakReference<symbol_Tester>) e).get();
    if (sym == null) {
      O e = call(masterSymbol_map, 'getEntry, tester.symbol.master);
      MasterSymbol existingMaster = e == null ? null : ((WeakReference<MasterSymbol>) e).get();
      if (existingMaster != null)
        tester.symbol.master = existingMaster;
      else
        masterSymbol_map.put(tester.symbol.master, true);
      symbol_map.put(sym = tester, true);
    }
    ret sym.symbol;
  }
  endifndef
}

static Symbol symbol(CharSequence s) {
  if (s == null) null;
  ifdef SymbolAsString
  ret str(s);
  endifdef
  ifndef SymbolAsString
  if (s instanceof Symbol) ret (Symbol) s;
  if (s instanceof S) ret symbol((S) s);
  ret symbol(str(s));
  endifndef
}