Could I ask for some confirmation about this? I have some flows calling `mapLatest`/ `tranformLatest...

# coroutines

[Chris Fillmore]

Could I ask for some confirmation about this? I have some flows calling `mapLatest`/ tranformLatest etc, and I want to create a CoroutineScope that is cancelled when these flows are cancelled. So, roughly:

myFlow
  .mapLatest {
    val scope = CoroutineScope(currentCoroutineContext().job)
    // returns something that uses `scope`
  }

So, my expectation is that when myFlow emits, scope will be cancelled. That’s correct?

[Joffrey]

Could you please elaborate on what you're doing with the scope? From just this snippet, I see no reason why the flow or the mapLatest operator would be aware of this scope, and thus no way it could possibly cancel it. So I guess what follows matters.

[Chris Fillmore]

myFlow
  .mapLatest {
    val scope = CoroutineScope(currentCoroutineContext().job)
    return SomeObject(
      state = anotherFlow.stateIn(scope, ...)
    )
  }

// elsewhere, in my UI
val someObjectState by someObject.state.collectAsState()

Something like this. A StateFlow is collected in that scope.

(P.S. I don’t love this but it’s some older code and it’s how I did it.)

[Chris Fillmore]

It looks like what I’m trying to do is propagate cancellation via the coroutine context.

[Chris Fillmore]

myFlow
  .mapLatest {
    coroutineScope {
      SomeObject(
        state = anotherFlow.stateIn(this, ...)
      )
    }
  }

This would propagate cancellation but mapLatest will never emit, of course

[Chris Fillmore]

I’m wondering if it’s possible to do what I’m trying to do

[Chris Fillmore]

Oh, I could do

myFlow
  .transformLatest {
    coroutineScope {
      emit(Someobject(
        state = anotherFlow.stateIn(this, ...)
      ))
    }
  }

Sorry I know this is ugly as sin but I don’t have the bandwidth to fix all this right now

[Trevor Stone]

could you use flatMapLatest instead? I guess a lot of it depends on if the final item you're emitting needs to have a scope internally, or if this is for intermediary steps. Emitting an item bound to the flow's scope itself seems like bad practice

[Chris Fillmore]

I think a slight refactoring would make use of combine and remove the StateFlow from “SomeObject” in the example code

[Chris Fillmore]

I just haven’t gotten around to it