anchor.diff:    int get hashCode => identityHashCode(value);
   }
   
  -typedef void GlobalKeyUpdateListener(GlobalKey key, Element element);
   typedef void GlobalKeyRemoveListener(GlobalKey key);
   
   /// A GlobalKey is one that must be unique across the entire application. It is
  
positive.code:         throw message;
        return true;
      });
      if (_updatedKeys.isEmpty && _removedKeys.isEmpty)
        return;
      try {
        for (GlobalKey key in _updatedKeys) {
          Element element = _registry[key];
          if (element != null && _updateListeners.containsKey(key)) {
            Set<GlobalKeyUpdateListener> localListeners = new Set<GlobalKeyUpdateListener>.from(_updateListeners[key]);
            for (GlobalKeyUpdateListener listener in localListeners)
              listener(key, element);
          }
        }
        for (GlobalKey key in _removedKeys) {
          if (!_registry.containsKey(key) && _removeListeners.containsKey(key)) {
            Set<GlobalKeyRemoveListener> localListeners = new Set<GlobalKeyRemoveListener>.from(_removeListeners[key]);
  
negative.code:     _registry[this] = element;
    }
  
    void _unregister(Element element) {
      assert(() {
        if (_registry.containsKey(this) && _debugDuplicates.containsKey(this)) {
  