anchor.diff:  import 'basic.dart';
   import 'provider.dart';
   
  -class _ExtraMixin {
  +mixin _ExtraMixin {
     Map<String, Object> _extra;
     Map<String, Object> get extra => _extra ??= <String, Object>{};
   }
  
positive.code: 
    @override
    BuildContext get context {
      assert(_throwIfDisposed());
      return _buildContext;
    }
  
  
negative.code:   @override
    Widget buildComponent(String name) {
      assert(name != null, 'The name must be NotNull for buildComponent.');
      final Dependent<T> dependent = logic.slot(name);
      final Widget result = dependent?.buildComponent(store, getState) ??
          store.buildComponent(name);
      assert(result != null, 'Could not found component by name "$name."');
  