How would y'all register a callback on an element ...

# coroutines

[reactormonk]

How would y'all register a callback on an element getting passed along in a Flow (think Flow<Card>) - the callback should fire after the card has been disconnected. I'm currently on interface Card { var afterCardRemoval: Function<Unit>? } and then firing from the scope producing the Flow<Card>, but that feels kinda dirty.

[Joffrey]

I don't think I understand the question. What does the flow have to do with the question? Are you asking about how to register the callback or how to fire it?

For instance, why doesn't .onEach { afterCardRemoval = { ... } } work for you?

[Robert Williams]

Are you sure it wouldn't work better as a Flow<Event> where Event can be CardDetected, CardRemoved etc?

[reactormonk]

https://kotlinlang.slack.com/archives/C1CFAFJSK/p1657876089729049?thread_ts=1657875875.988959&amp;cid=C1CFAFJSK
That was my first approach as well, but I was wondering if I could associate it by callback instead of the consuming application having to do the association

[reactormonk]

... how do you even reply to specific replies in slack?

[reactormonk]

For instance, why doesn't .onEach { afterCardRemoval = { ... } } work for you?

there's basically the Flow<Event> which I'm processing, and I'm wondering if I can change the API a bit.

[Robert Williams]

Yeah, unfortunately it's pretty application specific what makes the most sense for your consuming code but I agree callbacks feel a little clumsy when you're already working with coroutines

[Robert Williams]

Another option would be to add a Lifecycle flow inside Card which they could subscribe to separately

[reactormonk]

That's an option, is there one which I can use to send a single value, then finishes?

[Robert Williams]

A StateFlow might work well here because it means if I ever have a Card from anywhere I can always check if the current state is Active or Removed, as well as the original use case of listening for removal

[reactormonk]

I've tried with a MutableStateFlow, but there's a) how do I clean it up, aka how do I set the Flow from the state to over? Make it a take() is my current approach, but I'm not sure I like it. Also, how do I fire off an async into the sunset? the coroutineScope { async { flow.collect { ... } } } doesn't yield as I'd expect it to.

[gildor]

If you want Flow over just cancel it (or use operators like first()/until() which will close it on some event
You cannot cancel MutableStateFlow btw, so it's not probably what you beed

[gildor]

Also flow implementation itself can cancel itself after some event