what is the recommended way of achieving callbacks in Kotlin Multiplatform? Via coroutines?

are you talking about at the borders of your shared code and platform code?

For example for interfaces in the common code, that are implemented in platform specific code

gotcha yeah so if you're using 1.3, coroutines will work fine on Android, but you end up needing to use callbacks on other platforms

We have a KMP supporting Android and iOS. We have a class called

Observer

that is in the common shared code and accepts a plain lambda for iOS or a suspend lambda for Android. These lambdas are the callbacks for `Flow`s emitting data, or, if you want, for a suspend-fun returning a value.

why needing to use callbacks on other platforms? coroutines don't have an equivalent on iOS for example?

correct, swift doesn't have a coroutine like facility yet

are there any samples online around this?

This is the setup I use with just pure coroutines. Check out the "Presentation layer" section. Much more flexible than callbacks and I find it cleaner than observers. It also works on iOS well.

Thanks for sharing. Went over quickly, but mentions "We don’t show any loading indicator, because there’s on big issue: Kotlin/Native does not support multithreading at the moment. This means, all of our code has to run on the main thread, therefore a loading indicator doesn’t make much sense when we’re doing network on the main thread." - so you're doing everything on main thread on iOS?

There are experimental coroutine lib versions with native mt:

1.3.5-native-mt

and a few other versions…., they are mentioned in that 462 issue

Oh yeah, I forgot about that. I had to implemented a custom iOS dispatcher with code I lifted from here that will allow async coroutines. Then create your coroutine scopes using that dispatcher. I'm not sure how the experimental lib works though, as Anton pointed out.

The experimental lib provides the multi-threaded

Dispatchers.Default

to your common code. If you are interested in doing KMP for Android and iOS only, take a look at TouchLab’s KaMP-Kit for guidance.

^^ yeah, if you can get that working it's for sure better than my hack.

so does 1.3.5-native-mt actually provide multithreading on iOS? i couldn't find any documentation on the release and have been reading through github for a while trying to figure it out

There's documentation within the branch at https://github.com/Kotlin/kotlinx.coroutines/blob/native-mt/kotlin-native-sharing.md

cool, so it sounds like at least some basic ability to run coroutines on a background thread is supported on all platforms with Dispatchers.Default implemented, with the caveat that it's currently a single background thread.. does that sound right?

Also with the caveat that it doesn't rescue you from needing to handle things getting frozen when crossing threads

thanks, that's very helpful

1.4 support and whatever bugs they've fixed in the meantime. If you want more detail you're mostly stuck digging through issues and commit messages (or looking at the code directly)

yeah, i've been doing that quite a bit, was hoping to get my head out of the weeds to see if someone could help at a higher level.