anchor.diff:    ExternalClass._();
   
     factory ExternalClass([updates(ExternalClassBuilder b)]) = _$ExternalClass;
  -
  -  factory ExternalClass.build(
  -      {String docComment,
  -      String name,
  -      SetBuilder<TypeParameter> genericTypes}) {
  -    return (new ExternalClassBuilder()
  -          ..docComment = docComment
  -          ..name = name
  -          ..genericTypes = genericTypes ?? new SetBuilder<TypeParameter>())
  -        .build();
  -  }
   }
   
   abstract class ExternalClassBuilder
  
positive.code:   GenericType._();
  
    factory GenericType([updates(GenericTypeBuilder b)]) = _$GenericType;
  
    factory GenericType.build(
        {String docComment,
        String name,
        Classifier base,
        MapBuilder<TypeParameter, Classifier> genericTypeValues}) {
      return (new GenericTypeBuilder()
            ..docComment = docComment
            ..name = name
            ..base = base
            ..genericTypeValues =
                genericTypeValues ?? new MapBuilder<TypeParameter, Classifier>())
          .build();
    }
  }
  
  abstract class GenericTypeBuilder
  
negative.code:   ValueClass._();
  
    factory ValueClass([updates(ValueClassBuilder b)]) = _$ValueClass;
  }
  
  abstract class ValueClassBuilder
  