Allow sync access to value of combined BehaviorSubjects

[smkhalsa]

I'm composing multiple BehaviorSubjects using CombineLatestStream, and I'd like to be able to get sync access to the combined result immediately after adding an event to one of the origin BehaviorSubjects.

final subject1 = BehaviorSubject.seeded(0);
final subject2 = BehaviorSubject.seeded(0);
final combined =
    CombineLatestStream.combine2(subject1, subject2, (a, b) => a + b)
        .shareValue();

subject1.add(1);

expect(combined.value, equals(1));

[hoc081098]

Currently not supported :(

[HannibalKcc]

@hoc081098 Hi, this issue has been opened so many days. Do you think we need support combine BehaviorSubjects?

I want to try to achieve it.

[frankpepermans]

It might be hard to implement, since rxdart builds upon plain Dart streams, however, if both BehaviorSubjects are sync=true, then it might be doable,

Did you test the example with that sync value set to true?

[HannibalKcc]

@frankpepermans
set BehaviorSubject.sync = true will not be doable.

ValueStream must be listened and wait nextTick e.g. await Future.delayed(Duration(seconds: 0), cb).

    final s1 = BehaviorSubject.seeded(0, sync: true);
    final s2 = BehaviorSubject.seeded(0, sync: true);

    final combined =
        Rx.combineLatest2(s1, s2, (int a, int b) => a + b).shareValue();
    s1.add(1);
    combined.listen(expectAsync1((res) => expect(res, 1)));

    final stream =  Stream.fromIterable([1, 2, 3]).shareValue();
    stream.listen((_) {});

    print('combined ${combined.value}'); // null
    print('stream ${stream.value}'); // null
    await Future.delayed(Duration(seconds: 0), () {
      print('combined ${combined.value}'); // 1
      print('stream ${stream.value}'); // 3
    });