what would be a recommended way of registering a callback for the scope cancellation (or all childre...

# coroutines

[Maciek]

what would be a recommended way of registering a callback for the scope cancellation (or all children)? Would the empty callbackFlow with awaitClose work here?

fun CoroutineScope.onCancel(action: () -> Unit) {
        callbackFlow<Unit> { 
            awaitClose(action)
        }.launchIn(this)
    }

[Joffrey]

I think it would be more correct to access the Job from the scope's context:

fun CoroutineScope.onCancel(action: () -> Unit) {
    coroutineContext.job.invokeOnCompletion { ex ->
        if (ex is CancellationException) {
            // do stuff
        }
    }
}

[Maciek]

indeed it looks better, thanks!

[Joffrey]

There is an overload of invokeOnCompletion that you could use, but I'm not very familiar with it, so please read the docs 😉

[Joffrey]

Also, it might be important to note that not all `CoroutineScope`s have a Job in their contexts, in which case coroutineContext.job will fail. You can use coroutineContext[Job] instead if you want to get a nullable Job? instead and deal with it.
If there is no Job, there is also no structurred concurrency, so I guess your use case only makes sense on scopes with a Job, but still good to know

[Maciek]

yeah, I was wondering how the scope construction might impact that code, thanks for pointing that out