I need advice on something: ```sealed class Update...

# coroutines

[myanmarking]

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

[gildor]

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

[myanmarking]

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

[gildor]

why you cannot duplicate?

[gildor]

anyway, share operators are not released yet

[myanmarking]

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

[gildor]

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

[gildor]

cannot have two calls to the same parent flow

But why?

[gildor]

what if someone will do that?

[gildor]

or even consume your dispatchUpdates() twice?

[gildor]

it would be the same

[myanmarking]

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

[myanmarking]

i'll use a channel. its more appropriate then

[gildor]

so your existing solution will not work too

[gildor]

I mean it doesn’t limit amount of subscribers

[gildor]

I would implement for now using BroadcastChannel

[myanmarking]

yes, it does not

[gildor]

and use asFlow() on it

[gildor]

so it would support multiple subscribers

[gildor]

and reimplement later with Flow share operator

[ahulyk]

@myanmarking try StateFlow . I did some simple sample -> https://pl.kotl.in/CIFp67rcr

[myanmarking]

ok thanks. i'll give it a try

[gildor]

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