IssueTracker

saveable has built-in support for Coroutines' MutableStateFlow, supporting the following use case:

val state by saveable { MutableStateFlow(...) }

It does this by providing an overloaded function that handles MutableStateFlow.value and serializes it when needed.

To help people migrate from saveable to saved, we want to support MutableStateFlow in our KotlinX serialization support.

While working on getMutableStateFlow CL, I experimented with this idea and created a naive KSerializer implementation to handle MutableStateFlow.

Here’s what it could look like:

private class StateFlowSerializer<T : Any>(val valueSerializer: KSerializer<T>)

public inline fun <reified T : Any> stateFlowSerializer(): KSerializer<StateFlow<T>>

For serialization, we would use (value as MutableStateFlow<T>).value + valueSerializer to serialize the content. Deserialization works in the opposite direction.

Here’s a usage example:

val state by saved(serializer = stateFlowSerializer<Int>()) { MutableStateFlow(1) }

However, calling this without the serializer would cause an exception.

Our variant should work like saveable: if T (the generic type in saved) is serializable, it should work without needing the serializer.

The goal is to find the best way to support MutableStateFlow in saved.

Related to b/378895074.