Can someone help me understand.. If I want to cre...

# coroutines

[Tim Malseed]

Can someone help me understand..

If I want to create a StateFlow, I can call MutableStateFlow(). But, if I want to convert a Flow into a StateFlow, I call stateIn().

stateIn() requires a CoroutineScope . But MutableStateFlow() doesn’t. Why is that?

[Joffrey]

Using MutableStateFlow is like creating a variable which you can set. It doesn't require any coroutine.

However, if you want to create a StateFlow out of an existing Flow, you need somehow to collect elements from that flow so you can set the value of the state flow. Using stateIn creates a coroutine which does exactly that, hence the need for a scope.

You can see stateIn as a sort of shortcut for:

val stateFlow = MutableStateFlow(initialValue)
scope.launch {
    flow.collect {
        stateFlow.value = it
    }
}

So as you can see, you need more than just MutableStateFlow to do what stateIn does

[Tim Malseed]

Oh yeah I see. Thanks for a great explanation!

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

The flow code is quite readable and is often a great way to answer these sorts of questions: https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/common/src/flow/operators/Share.kt