anchor.diff:  }
   
   /// A [GlobalView] for an [Entity] that does not have globals.
  -class _EmptyGlobalView implements GlobalView {
  +class _EmptyGlobalView extends GlobalView {
   
     static const _singleton = const _EmptyGlobalView._useFactoryInstead();
   
  
positive.code:   }
  }
  
  /// A view of globals as they relate to a specific [Entity]. Implements
  /// observability based on dependencies of the globals involved.
  abstract class GlobalView extends Observable implements Map {
    /// A real global view backed by a map of registered globals.
    factory GlobalView(EntityWrapper entity,
        Map<String, GlobalRegistration> globals) =>
  
negative.code:   operator[](String key);
  }
  
  class _GlobalViewImpl extends ChangeNotifier with _FakeMap implements GlobalView {
  
    EntityWrapper _entity;
    Map<String, GlobalRegistration> _globals;
  