Hello, World! When using `suspendCancellableCoroutine` I sometimes see code that calls `cont.resume...

# coroutines

[bod]

Hello, World! When using suspendCancellableCoroutine I sometimes see code that calls cont.resume(result) but when I try that, it's looking for a onCancellation argument, I so I need to do cont.resume(result) {} instead. Ideas why? (May be relevant: I'm in Kotlin-js).

[Dominaezzz]

The first resume needs an import I think. (It's an extension function).

[bod]

Thought of it but couldn't find the right one, and IJ didn't help. But I finally found it:

import kotlin.coroutines.resume

😄 Thanks!

[Orhan Tozan]

I thought that if you dont need the cancellation exception, you use suspendCoroutine instead of suspendCancellableCoroutine?

[Dominaezzz]

Yes. I assume that cont.invokeOnCancellation is being used.

[bod]

turns out I was using suspendCancellableCoroutine when I could use suspendCoroutine 🙂 Thanks a lot

[louiscad]

Well, suspendCoroutine is when you cannot and don't want to support cancellation at all, which can lead to memory leaks in some cases if your code never resumes or resumes after a long time while it should have been cancelled.

[louiscad]

So, I tend to think the opposite scenario is more correct: one might use suspendCoroutine when suspendCancellableCoroutine could/should be used.

[Orhan Tozan]

With supporting cancellation, do you mean passing something like removeEventListener to the onCancellation?

[louiscad]

@Orhan Tozan There's multiple ways of doing it. You mentioned one way to do it. Basically, you need to unregister or cancel the callback, and do it from onCancellation or in a `try`/`finally` or `try`/`catch(e: CancellationException)` block surrounding the suspendCancellableCoroutine call.

Here's a real world example that allows to wait for a click on a View in an Android app: https://github.com/LouisCAD/Splitties/blob/49e2ee566730aaeb14b4fa9e395a677c3f214dba/modules/views-coroutines/src/androidMain/kotlin/splitties/views/coroutines/VisibilityAndClicks.kt#L34-L51