Can`t mixin class with extended mixin

[ChaserVasya]

my helper file

import 'dart:async';
import 'package:bloc/bloc.dart';

mixin MyEventInterceptor<E, S> on _EventHandlerIntercepted<E, S> {
  S createErrorState(AppException e);

  @override
  _interceptor(handler, emit) async {
...
  }
}

mixin _EventHandlerIntercepted<Event, State> on Bloc<Event, State> {
  @override
  void on<E extends Event>(
    handler, {
    transformer,
  }) {
    return super.on(
      (event, emit) => _interceptor(() => handler(event, emit), emit),
      transformer: transformer,
    );
  }

  FutureOr<void> _interceptor(
    FutureOr<void> Function() handler,
    Emitter<State> emit,
  );
}

my bloc code

class MyBloc
    extends Bloc<MyEvent, MyState>
    with MyEventInterceptor<MyEvent,   MyState> {
...
}

error:

'MyEventInterceptor<MyEvent, MyState>' can't be mixed onto 'Bloc<MyEvent, MyState>' because 'Bloc<MyEvent, MyState>' doesn't implement '_EventHandlerIntercepted<MyEvent, MyState>'. (Documentation)  Try extending the class 'MyEventInterceptor<MyEvent, MyState>'.

dart 3.2.0

[lrhn]

That is working as currently specified.
As the error says, Bloc doesn't implement _EventHandlerIntercepted, so you cannot apply MyEventInterceptor to it.

If you're asking for this to work, then it's really a request for composite mixins, where MyEventInterceptor would somehow be declared as including the _EventHandlerIntercepted mixin, and mixing it in will apply both.
(That will require new syntax, the current declaration already has a specific meaning.)

There is an existing issue for mixin composition, #540, do we'll defer to that.

[TekExplorer]

That is working as currently specified. As the error says, Bloc doesn't implement _EventHandlerIntercepted, so you cannot apply MyEventInterceptor to it.

If you're asking for this to work, then it's really a request for composite mixins, where MyEventInterceptor would somehow be declared as including the _EventHandlerIntercepted mixin, and mixing it in will apply both. (That will require new syntax, the current declaration already has a specific meaning.)

There is an existing issue for mixin composition, #540, do we'll defer to that.

Why would that need new syntax? wouldnt mixin [class] MyMixin with OtherMixin, Mixin2 {} be enough? It's a compiler error to do this now.

[lrhn]

Well, that is new syntax, since a mixin or mixin class cannot have a with clause today.
It doesn't have to very different new syntax, preferably not, just some syntax which doesn't already have a meaning that we'd have to change.

[TekExplorer]

Well, that is new syntax, since a mixin or mixin class cannot have a with clause today. It doesn't have to very different new syntax, preferably not, just some syntax which doesn't already have a meaning that we'd have to change.

fair enough.