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kotlinlang

Hello, World! Is there an easy way to implement `MutableStateFlow`? For instance, does something similar to `callbackFlow {}` exist?

Hi! I'd like to expose some kind of persisted data (Android's SharedPreferences) as `MutableStateFlow` s

I managed to do it by having a wrapped `MutableStateFlow` but that involves quite a bit of boilerplate

You can transform any flow (e.g. callbackFlow) into StateFlow via flow.stateIn

oh but that creates a non mutable `StateFlow` though - my need is for a mutable one.

yep, you cannot return data back using  stateIn

I think the easiest solution is just create a standard MutableStateFlow() and allow update it from two sides

You can do something like this:
```class FlowPreferences {
    private val flows = HashMap&lt;String, MutableStateFlow&lt;Any&gt;&gt;()
    private val sharedPreferences = TODO()
    private val someScope: CoroutineScope = TODO("Lifecycle of this scope really depends on your case, it can be just GlobalScope, if preferences are global")
    fun stringFlow(key: String): MutableStateFlow&lt;String&gt; {
        flows.getOrPut(key) {
            MutableStateFlow&lt;String&gt;(sharedPreferences.getString(key)).apply {
                someScope.launch {
                    collect {
                        if (sharedPreferences != it) {
                            sharedPreferences.edit().putString(it).apply()
                        }
                    }
                }
                //TODO: it also possible observe sharedPreferences and update flow
            }
        }
    }
}```

Though, I’m not sure that having hot flows for this case is right solution, I would just replace this with non-mutable StateFlow and additional method for update, yes, a bit more code, but easier to maintain and clear separation of observable state from updating of this state (they also could be parts of separate interfaces)

you can see here how I did it (the wrapping approach), to compare: <https://github.com/BoD/android-kprefs/blob/mutable-state-flow/library/src/main/kotlin/org/jraf/android/kprefs/PreferenceFlowProperty.kt#L68>