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:     _parent = parent;
      _slot = newSlot;
      _depth = _parent != null ? _parent.depth + 1 : 1;
      assert(() { _debugLifecycleState = _ElementLifecycle.mounted; return true; });
    }
  
  
negative.code: 
    static final Map<GlobalKey, Element> _registry = new Map<GlobalKey, Element>();
    static final Map<GlobalKey, int> _debugDuplicates = new Map<GlobalKey, int>();
    static final Map<GlobalKey, Set<GlobalKeyRemoveListener>> _removeListeners = new Map<GlobalKey, Set<GlobalKeyRemoveListener>>();
    static final Set<GlobalKey> _removedKeys = new Set<GlobalKey>();
  
    void _register(Element element) {
      assert(() {
        if (_registry.containsKey(this)) {
  