!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));
}