I’m having a problem implementing a kotlin `suspen...

# multiplatform

[Matheus Finatti]

I’m having a problem implementing a kotlin suspend function in Swift
I have an interface, e.g.:

interface Loader {
    suspend fun fetch()
}

which I implement in Android and in iOS.
The iOS version looks like this:

public class RemoteFeatureLoader : Loader {
    public func fetch(completionHandler: @escaping (KotlinUnit?, Error?) -> Void) {
        
        doAsyncStuff { [weak self] in
            completionHandler(KotlinUnit(), nil)
        }
    }
}

And the caller in the shared code looks like this

class CommonLoader() {
    override suspend fun fetch() {
        localFeatureLoader.fetch()
        remoteFeatureLoader.fetch()
    }
}

and finally, the CommonLoader.fetch() is being called from a view model which is also shared

class CommonViewModel(
    private val scope: CoroutineScope,
    private val uiContext: CoroutineContext,
) : ViewModel {

    override fun startup() {
        scope.launch(context = uiContext) {
            loader.fetch()
        }
    }
}

Basically, the Android version works like a charm, but the iOS version hangs at loader.fetch()
If I add a log after remoteFeatureLoader.fetch() it is printed just fine, but the function never returns/resumes from its suspended state.

Does anyone have any clue what could be going on? I appreciate any help! Thank you!

[ankushg]

Also curious about this.

We currently declare any interface intended to be implemented outside of Kotlin with a callback-based API. This lets us pretty easily implement them in Swift.

We then convert the callbacks to `suspend fun`s within our KMP codebase, so we can use coroutines within Kotlin.

[Matheus Finatti]

This is the suggested approach given by my teammate as well

Implementing my interface in Swift gave me two options:

public func fetch() async throws -> KotlinUnit

and

public func fetch(completionHandler: @escaping (KotlinUnit?, Error?) -> Void)

I couldn’t try the first one as it is only for iOS 15 at the moment, but the second one should theoretically work

[ankushg]

Yeah... I think the suspend fun -> completionHandler mapping is only be unidirectional (Kotlin -> Swift) and may not be supported in the opposite direction

[mittapalli hareesh]

@Matheus Finatti Hi, I am also developing KMM suspend fun.

I too decided to use callbacks instead of coroutines since swift doesn’t support coroutines for now.

can you please let me know how u have done callbacks in ios (KMM) ?

@ankushg / @Matheus Finatti please share any gitHub or reference code base if you came across, waiting for you guys response, Thanks !!