Allow AsyncSignal to be used manually as well

[rivella50]

At the moment AsyncSignal has no public constructor and can only be used in combination with a Future or a Stream, where the determination of the possible states (value, loading, reloading, error) are performed internally.
Sometimes i have cases where that async procedure is not possible, e.g. when using fpdart for data requests, where i get back e.g. a Future<Either<ApiException, List<Post>>> type, which imo cannot be handled by AsyncSignal.
Therefore it would be great to see if AsyncSignal could allow setting its states (currently _AsyncState) and corresponding data (value, exception) from outside as well in order to have 3 ways of using AsyncSignal (from Future, from Stream and manually).

[rodydavis]

This is an interesting example, could you provide some more code as an example?

[rivella50]

Sure, this is a controller which is requested by a view widget to get some posts from a service/provider:

class PostsController {
  final PostsService postService = PostsService();
  final signal = AsyncSignal(initialValue: <Post>[]);

  Future<void> getPosts() async {
    /// Future<Either<ApiException, List<Post>>>
    final result = await postService.getPosts();
    result.mapLeft((a) => signal.state = AsyncError(a, StackTrace.current);
    result.map((list) => signal.state = AsyncData(list));
  }
}

I added some pseudo code regarding AsyncSignal.
This would be again similar to what Riverpod offers in its AsyncNotifier class.

[jinyus]

@rivella50 Since you're assigning the states manually, why not use a regular signal?

final signal = signal<AsyncValue>(AsyncData(<Post>[]))

Future<void> getPosts() async {
    /// Future<Either<ApiException, List<Post>>>
    signal.value = AsyncLoading();
    final result = await postService.getPosts();
    result.mapLeft((a) => signal.state = AsyncError(a, StackTrace.current);
    result.map((list) => signal.state = AsyncData(list));
}

[rivella50]

Sure, that would be possible. I just thought why having those data structures (AsyncValue etc.) separated (or even worse: adding an additional package like Riverpod) if everything would be already available and centralized within AsyncSignal?

[rivella50]

So if the maintainers of Signals don't want to go for this i would solve it with what @jinyus suggested (i've seen that your own state management plugin also has an implementation of AsyncValue and its child classes).
But i just want to mention that imo there can be situations where it makes sense letting developers manually modify the state of AsyncSignal - handling this internally and only for Futures and Streams might not be enough. But let's see what the future brings.

[rodydavis]

Now fixed with AsyncState in 2.0.3

[Solido]

This is the behavior of the Inject << operator that we use on ListSignal
When dealing with AsyncSignal you would be able to do

postsSignal << [Post(id:1,message:"received"),Post(id:2,message:"received"),] 

What could be the best returned value?

void operator <<(Iterable<T> other) 

import 'package:signals/signals.dart';

void main() {
  final s1 = Stream.fromIterable([1, 2, 3]);

  final resolve = asyncSignalFromFuture(
      () => Future.delayed(Duration(seconds: 1), () => true),
      initialValue: false);

  final as1 = asyncSignalFromStream(() => s1, initialValue: 0);

  effect(() {
    if (resolve()) as1 << [4, 5, 6];
  });

  effect(() {
    final rs = as1();
    print("$rs");
  });
}

[rodydavis]

Working on a big refactor to AsyncSignal and it will allow for manual usage:

#78