I need advice on something:

sealed class Updates{
    data class LiveUpdate(val progress: Int): Updates()
    data class History(val list: List<Int>): Updates()
}

private fun fetchUpdates(): Flow<Updates> {
    TODO()
}

private fun save(list: List<Updates.History>){
    TODO()
}

fun dispatchUpdates(): Flow<Updates.LiveUpdate>{
    val history = mutableListOf<Updates.History>()
    return fetchUpdates()
        .onEach { 
            if(it is Updates.History){
                history.add(it)
            }
        }
        .onCompletion { if(it != null) save(history) }
        .filterIsInstance<Updates.History>()
}

Is there any way to improve this code so that the save part doesn't end up a side-effect? Something like an inner flow. I'm not sure how to approach this

To avoid side efffects you shouldn’t mix sideffect with this chain. and instead have 1 flow for updates and 1 for side effect:

fun historyUpdates(): Flow<Updates.History> {
  return fetchUpdates().filterIsInstance<Updates.History>()
}

suspend fun saveHistory() {
  save(historyUpdates().toList())
}

//and some other method which want to get updates on every update, but without mixing with side effect

yes, it makes sense. but parent flow is a callback flow, so i cannot duplicate the stream. I need to branch it into two independent flows, but idk how to do that

why you cannot duplicate?

yes, thats it. cannot duplciate because i cannot have two calls to the same parent flow. won't work

so now or start 2 flows, or use channel, or keep your existing code

because its a wrapper for some ble operations. and it cannot happen at the same time. its a legacy api

so your existing solution will not work too

yes, it does not

and use asFlow() on it

@myanmarking try

StateFlow

. I did some simple sample -> https://pl.kotl.in/CIFp67rcr

ok thanks. i'll give it a try

StateFlow will not help in this case, it will not help with laziness and cancellation, which needs you for ble events And after all StateFlow is caching the latest event, which is not what you need probably for events listening