!7

sclass Symbol {
  S text;
  
  *() {}
  *(S *text, bool dummy) {} // weird signature to prevent accidental calling
  
  public int hashCode() { ret main.hashCode(text); }
  toString { ret text; }
  public bool equals(O o) {
    ret this == o;
  }
}

sclass SymbolTester {
  S text;
  
  *() {}
  *(S *text) {}
  
  public int hashCode() { ret main.hashCode(text); }
  public bool equals(O 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) {
    // This is a trick that works because of how WeakHashMap compares keys.
    SymbolTester test = new(s);
    //WeakHashMap2.Entry<Symbol, Bool> e = symbolMap.getEntry(test);
    //Symbol sym = e == null ? null : e.get();
    O e = call(symbolMap, 'getEntry, test);
    Symbol sym = e == null ? null : ((WeakReference<Symbol>) e).get();
    if (sym == null)
      symbolMap.put(sym = Symbol(s, false), Bool.TRUE);
    ret sym;
  }
}

p {
  S s1 = "a", s2 = lower("A");
  assertNotIdentical(s1, s2); // Now more clearly showing the improvement
  Symbol a = symbol(s1);
  Symbol a2 = symbol(s2);
  assertEquals("a", str(a));
  assertEquals("a", str(a2));
  assertIdentical(a, a2);
  Symbol b = symbol("b");
  assertEquals("b", str(b));
  print("OK");
}

Began life as a copy of #1010604