!7

//!include #1010605 // WeakHashMap2

sclass Symbol {

  S text;

  bool test;

  *() {}

  *(S *text, bool *test) {} // weird signature to prevent accidental calling

  public int hashCode() { ret main.hashCode(text); }

  toString { ret text; }

  public bool equals(O o) {

    if (!test) ret this == o;

    ret o instanceof Symbol && eq(text, o/Symbol.text);

  }

}

static new WeakHashMap<Symbol, Bool> symbolMap;

static Symbol symbol(S s) {

  if (s == null) null;

  synchronized(symbolMap) {

    Symbol test = Symbol(s, true);

    //WeakHashMap2.Entry<Symbol, Bool> e = symbolMap.getEntry(test);

    //Symbol sym = e == null ? null : e.get();

    O e = call(symbolMap, 'getEntry, test);

    Symbol sym = cast callOpt(e, 'get);

    if (sym == null)

      symbolMap.put(sym = Symbol(s, false), Bool.TRUE);

    ret sym;

  }

}

p {

  Symbol a = symbol("a");

  Symbol a2 = symbol("a");

  assertEquals("a", str(a));

  assertEquals("a", str(a2));

  assertIdentical(a, a2);

  Symbol b = symbol("b");

  assertEquals("b", str(b));

}