Getting Option> unpacked in Flutter

Question

In my bloc state I have this:

Option<Either<T, Stream<T>>> optionFailureOrStream,

It' can be empty (Option) or have an error or a stream.

In my bloc I yielding this with optionOf like this:

 yield state.copyWith(optionFailureOrStream: optionOf(failureOrStream));

Now in my Widget I want to know if it has a value and if it has a value, I want to fold them to return two different screens:

 if (state.optionFailureOrStream.isSome()) {
    final optionFailureOrStream = state.optionFailureOrStream;

    optionFailureOrStream.map((a) => a.fold(
        (failure) => FailureWidget(failure: failure),
        (stream) => buildSaved(stream, context)));
}

But somehow I can't get rid of the Option<T> type. It complains about the wrong type.

The return type 'Option<Widget>' isn't a 'Widget', as required by the closure's context.dart(return_of_invalid_type_from_closure)

I assume there is a really easy way to do this. I am having a real hard time finding any dart/flutter related manuals and the source code of dartz isn't that self-explaining, if you are new to these concepts.

score 0 · Accepted Answer · answered Apr 28 '20 at 11:48

Widget func() {
  Option<Either<String, Stream<String>>>//I assume your failure is a string for example
      optionFailureOrStream; 
  return optionFailureOrStream.fold(
    () => Container(),//if none()
    (Either<String, Stream<String>> either)//if some(Either<String,Stream<String>>) 
    => either.fold(
      (String failure) => Container(),
      (Stream<String> stream) => Container(),
    ),
  );
}

note: this code is just for demonstration (if that is not clear), as you see I am not even initializing the variable but the code is just to demonstrate how you can return a value from an option without using an if statement

Getting Option> unpacked in Flutter

1 Answers1