How would you refactor this into a cold flow? ```private val version = MutableStateFlow(0L).also { s...

# coroutines

[Zoltan Demant]

How would you refactor this into a cold flow?

private val version = MutableStateFlow(0L).also { state ->
    scope.launch {
        registry.repositories.map { repository ->
            repository.changes
        }.merge().collect {
            state.update { version ->
                version.inc()
            }
        }
    }
}

[Sam]

Since you asked about a cold flow, I guess that means you don't need it to be a StateFlow? A bit more info would help, but it looks like this is just:

val version = registry.repositories
    .flatMapConcat { it.changes }
    .runningFold(0L) { acc, _ -> acc + 1 }

[Zoltan Demant]

No need for a StateFlow. Part of the challenge for me is that each repository.change is a Flow<...> and while I can use combine(flows) that will only emit after each flow has emitted a value I believe?

[Sam]

If you use flatMapConcat (or the now-deprecated merge) it will collect all the changes from the first repository before moving on to the next repository. If you want to collect changes from multiple repositories at the same time, you could use flatMapMerge instead.

[Zoltan Demant]

registry.repositories.map { it.changes }.merge().scan(0L) { version, _ ->
    version + 1
}

👍🏽 Thanks for the help, this clearly shows me that despite how much I work with and read about coroutines, I still have so much more to learn!