Hey! :wave: Is there any way to map values emitted by a `StateFlow` and still have a `StateFlow` and...

# coroutines

[Nacho Ruiz Martin]

Hey! 👋 Is there any way to map values emitted by a StateFlow and still have a StateFlow and not a Flow?
stateflow.map(::mapper) returns a Flow.

[Joffrey]

To have another StateFlow you would need to store a new state and to have a coroutine that collects the source flow into the new one. You could use stateIn after map to do that for you behind the scenes.

[Nacho Ruiz Martin]

😞 Ok, sounds a bit weird coming from Rx, but looks doable. Thanks!

[Joffrey]

What would you do in Rx? Also, why do you need a StateFlow as a result there (why is Flow not sufficient)?

[Nacho Ruiz Martin]

I need a StateFlow just to have better integration with Jetpack Compose.
In Rx a simple map on a BehaviourSubject would suffice, if I’m not mistaken.

[streetsofboston]

The return type of the map method on BehaviorSubject is a plain Observable (which is comparable to a plain Flow), which gives you the same type of problem that you are asking about.

http://reactivex.io/RxJava/3.x/javadoc/io/reactivex/rxjava3/subjects/BehaviorSubject.html

[Nacho Ruiz Martin]

🤔 You’re absolutely right.

[Martin Rajniak]

@Nacho Ruiz Martin FYI, you don't need StateFlow in JetpackCompose

You can collect Flow as state as well
https://developer.android.com/reference/kotlin/androidx/compose/runtime/package-summary#(kotlinx.coroutines.flow.Flow).collectAsState(kotlin.Any,kotlin.coroutines.CoroutineContext)

[Adam Powell]

You can, but you need to supply your own initial value since the collection doesn't begin until initial composition has completed

[Adam Powell]

Most of the time when people ask for this is because they are using StateFlow for hot state instead of snapshots, and snapshots can do this natively https://github.com/Kotlin/kotlinx.coroutines/issues/2631#issuecomment-859662590

[Adam Powell]

(example in the linked comment)

[Nacho Ruiz Martin]

Yes, that’s exactly my case, Adam. I ended up re-casting my Flow to StateFlow with stateIn. Feels a bit weird, but it works.

[hfhbd]

Although compose (Mutable) State is nice, the advantage using StateFlow is multiplatform support, especially iOS.