Given a `StateFlow<T>` instance, I want to log every emission of `T` from the source standpoin...

# coroutines

[zak.taccardi]

Given a StateFlow<T> instance, I want to log every emission of T from the source standpoint. Is this possible without duplicating logs for each subscriber?

[zak.taccardi]

We currently log at this point (before converting into a state flow):

[zak.taccardi]

.scan { .. }
.logEachState(logger)
.stateIn(scope)

But this will log duplicate values that are not emitted to subscribers.

We had a bug where T was not immutable and was not emitting when it’s var changed bc only the instance was mutated - (same instance will not be emitted twice in a row due to equality checks, even if the value changes)

[zak.taccardi]

if we logged at each subscriber, then we risk some real noisy logs

[Dominaezzz]

If I understand correctly, you basically want to swap line 2 and 3?

[zak.taccardi]

Yep, but it's a doOnNext() which returns a Flow<T> - and I want a StateFlow<T>

[Dominaezzz]

Hmm, okay I understand. I have an idea.

[Dominaezzz]

.scan { .. }
.stateIn(scope)
.apply { logEachState(logger).launchIn(scope) }

[Dominaezzz]

Oh wait, I'm guessing you don't want to log when there are no subscribers. If that's the case my code snippet won't work.

[Dominaezzz]

You could add a distinctUntilChanged() to your snippet I guess.

[Dominaezzz]

I have no other trivial ideas.

[stojan]

I guess you need something like this: https://kotlinlang.slack.com/archives/C1CFAFJSK/p1652287040843249

but for onEach

[DALDEI]

Reworked - <duh>
Expose your State flow like
// expose as
val state = flow { ...}
.stateIn(scope)
// Log with
private loggy = state.onEach {
log(it)
}.launchIn(..)