How do I choose between `CompletableDeferred` and `suspendCancellableCoroutine` when wrapping a call...

# coroutines

[mzgreen]

How do I choose between CompletableDeferred and suspendCancellableCoroutine when wrapping a callback based API into a coroutines API?
Here is an example of an API wrapped using `CompletableDeferred`: https://handstandsam.com/2022/02/28/install-referrer-kotlin-extension/
And here are examples of APIs wrapped using `suspendCancellableCoroutine`: https://chris.banes.dev/suspending-views/
When is the one approach preferable over the other one?

[Sam]

I would always recommend using suspendCancellableCoroutine. It's more lightweight, and it's also specifically designed for handling cancellation properly via continuation.invokeOnCancellation.

[Sam]

In the example that you shared using CompletableDeferred, I don't think the InstallReferrerClient connection will be cancelled when the coroutine is cancelled.

[Sam]

Whereas in the example with suspendCancellableCoroutine, you see this code:

// If the coroutine is cancelled, remove the listener
cont.invokeOnCancellation { removeOnLayoutChangeListener(listener) }

[Sam]

You probably could achieve something similar using CompletableDeferred.invokeOnCompletion, but it wouldn't be as clean

[mzgreen]

Thank you. Is there a way to check which one is "more lightweight" without knowing the internals?

[Sam]

suspendCancellableCoroutine is really the "primitive" on top of which all "await"-style suspending operations are built, so you can assume that using it directly is always the most lightweight option

[Sam]

In fact CompletableDeferred.await itself will end up calling something very similar to suspendCancellableCoroutine

[ephemient]

(it doesn't, it goes lower level than that)

[ephemient]

suspendCoroutine is probably the lowest level primitive that a user should typically see