Is there a way to map a `StateFlow<T>` to a `StateFlow<R>`? I have a `MutableStateFlow&l...

# coroutines

[Luke]

Is there a way to map a StateFlow<T> to a StateFlow<R>? I have a MutableStateFlow<MyEnum> in a view model, but I want it private to expose publicly a StateFlow<String>

[Javier]

.map?

[Luke]

It returns a Flow, not a StateFlow

[Luke]

But I would want basically that

[Javier]

maybe map + stateIn

[Luke]

Not bad. The only problem I have with this is that stateIn is a `suspend fun`… So I can’t assign my variable directly like a simple map would allow

[Luke]

Oh but not all stateIn are suspend fun

[streetsofboston]

How would that work?
If it would return a StateFlow<R>, how would the map function reverse map the latest value from a T to an R, when assigning a new value to that StateFlow<R> if it were implemented by a MutableStateFlow?

And this is just for map.
How would this work for filter? Etc..

Using stateIn helps by layering another statefull flow on top of the returned Flow

[rnett]

MutableStateFlow would need to go backwards, but I don't see a reason why you couldn't map a StateFlow backed by a MutableStateFlow into something like a ReadOnlyStateFlow.

[gildor]

"ReadOnlyStateFlow" is StateFlow, isn't?

[rnett]

I think the only actual implementation of StateFlow is MutableStateFlow (or rather StateFlowImpl, which stores a value). For map support, you would need a new implementation that doesn't store it's own state or support updates. But I think it would be exposed as just StateFlow, yeah.

[gildor]

StateFlow is Read only, same as List or Map are read only, not immutable

[rnett]

I thought it was too, but there's actually two classes that implement StateFlow: StateFlowImpl which also implements MutableStateFlow, and ReadonlyStateFlow that doesn't. Of course, ReadonlyStateFlow is just a wrapper around a StateFlow, so it has to be backed by a MutableStateFlow eventually, but I could see map being implemented using it. Any StateFlow implementation that supports map would need a different implementation that updates when it's source does, and wouldn't support writes.

[gildor]

mmap being implemented using it?

[gildor]

anyway, I really think that this attempt to make 2-way Flow is broken by definition