Has anyone ran into use cases for overloads of `Fl...

# coroutines

[Zach Klippenstein (he/him) [MOD]]

Has anyone ran into use cases for overloads of Flow operators for StateFlow that preserve the value property? I filed an issue for map here, curious if people have other use cases or use cases for other operators (or opinions about this proposal).
https://github.com/Kotlin/kotlinx.coroutines/issues/2081

[streetsofboston]

Why hot hold a second reference, a reference to the original StateFlow? Or collect the result Flow again, causing the current state to be collected?

I can imagine something like this for map, but it wouldn’t work for filter for example….

[streetsofboston]

I think the same is true for Rx; Calling map a Processor/Subject returns an Observable (or Flowable)

[Zach Klippenstein (he/him) [MOD]]

Yea, the number of operations this makes sense for is pretty small.

[Zach Klippenstein (he/him) [MOD]]

The difference from Rx is that Subject isn’t a read-only type, and isn’t suitable for exposing as such.

[Zach Klippenstein (he/him) [MOD]]

Why hot hold a second reference, a reference to the original StateFlow?

I’m not sure what you mean. For my use case, the underlying StateFlow is completely hidden as an implementation detail of a class, and only the more limited state subset is exposed.

[streetsofboston]

The class wrapping/hiding the StateFlow could expose a property getting its StateFlow’s `value`….

[Zach Klippenstein (he/him) [MOD]]

Doesn’t that defeat the purpose of having StateFlow as a separate, read-only type in the first place?

[streetsofboston]

I am playing the devil’s advocate here, I can see the usefulness, but it seems very very limited to me

[Zach Klippenstein (he/him) [MOD]]

I appreciate it, it also seems limited to me so I’m trying to play devils advocate on myself 😅

[Zach Klippenstein (he/him) [MOD]]

I can also do something like this, but it feels verbose and over-complicated for a simple map:

totalState.map { it.partialState }
  .stateIn(scope, initialValue = totalState.value.partialState)

[Zach Klippenstein (he/him) [MOD]]

It was just pointed out that this is a duplicate issue, and the original was closed with the rationale “Any chain of operators on a state flow can be materialized into another StateFlow using stateIn operator”, so that answers that.
https://github.com/Kotlin/kotlinx.coroutines/issues/2008#issuecomment-632614208

[bezrukov]

will not it a bit misleading since StateFlow provides distinctUntilChanged behavior?

I mean:
let's say stateFlow contains 0,1,2,3,4,5
stateFlow.map { it / 2 } will produce 0,1,2 which most likely unexpected there.

[Zach Klippenstein (he/him) [MOD]]

That seems like reasonable behavior. In my view, using StateFlow implies that the values being emitted represent “state”, and two states that are equivalent are not interesting.