Is it possible to get `MutableStateFlow<S>` from `MutableStateFlow<S?>`?

# coroutines

[Robert Jaros]

Is it possible to get MutableStateFlow<S> from MutableStateFlow<S?>?

[Ian Lake]

filterNotNull() + stateIn(). You need to pick either the version that specifies exactly what initialState you want when your MutableStateFlow<S?> is null or use the version that suspends until a non-null value becomes available

[Ian Lake]

Remember the whole contract of StateFlow is that it always has a value

[Robert Jaros]

But this way I can only get StateFlow<S> and I would like mutable version.

[Dominaezzz]

Make a new one and copy the value over.

[Ian Lake]

Ah, then you can probably follow the advice of this thread (doing the filterNotNull()) https://kotlinlang.slack.com/archives/C1CFAFJSK/p1612919750413900?thread_ts=1612919750.413900&cid=C1CFAFJSK

[Robert Jaros]

@Dominaezzz Thx, but I'm not sure a new stateflow is what I'm looking for. I would like to have a kind of "subview" to the orignal stateflow. So I could both change the original state value (of course with non-null values only) and get/collect the state value (non-nullable, with a given initial value in place of original nulls). I would like all collectors of the original stateflow to still get all the values. I'm thinking about a wrapper over new StateFlow<S> I get from the stateIn(), which maps setter call to the original stateflow, but it would require implementing MutableStateFlow interface, which is probably bad idea.

[Robert Jaros]

Probably I should think about it once again in the morning 😉

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

So you’re trying to map in both directions? I don’t think anything like that exists, but you could always just implement the interfaces yourself and make sure to satisfy all the contracts.