I notice `suspend` functions get translated to `async throws

Question

I notice `suspend` functions get translated to `async throws` automatically which is neet This however doesn t support cancellation i e when swift `Task` gets cancelled the source kotlin coroutine keeps on going In my local testing So why is this Is `async` function some sort of sideffect of objc rather than a deliberate kotlin native decision Can I somehow influence the `suspend gt async` adapter

ephemient · Answer

<https youtrack jetbrains com issue KT 47042> gt Cancellation dispatchers coroutine context task locals etc are not propagated between Kotlin and Swift they are discarded at the boundary between Kotlin and Swift

ephemient · Answer

I think this is inevitable for now because this is building on the Swift s automatic Objective C completion handler to async translation

ursus · Answer

so it just a sugar for the completion handler api

ephemient · Answer

yes <https developer apple com documentation swift calling objective c apis asynchronously>

ursus · Answer

okay so this necessarily doesn t have anything to do with kmm kn

ephemient · Answer

this could be addressed if K N generated Swift bindings instead of Objective C but that s still a ways off <https youtrack jetbrains com issue KT 49131>

ursus · Answer

hm how would that even work I d need a CoroutineScope to launch the suspend fun in exposed to Swift no

ephemient · Answer

I haven t seen any designs around it

ephemient · Answer

but Swift has its own optional structured concurrency that could be used perhaps by wrapping with <https developer apple com documentation swift withunsafecurrenttask body >

ursus · Answer

okay so to have cancellation the only way is to have some wrapper in kotlin which will own the coroutine scope launch the function in that scope and provide callback api + cancellation handle to swift

ursus · Answer

where I d wrap to async await with their coroutine builder thingy

ephemient · Answer

or some wrapper in Swift that turns its Task TaskGroup into a Kotlin CoroutineScope and then executes the Kotlin suspend fun with it

ephemient · Answer

it ll probably have to be optional though since there s uses of `suspend fun` that aren t kotlinx coroutines

ursus · Answer

I don t follow how is that possible with the current library

ursus · Answer

I thought all notions of `suspend` were stripped at the boundary

ephemient · Answer

in principle it s possible none of the code to do it exists afaik

Howie Nguyen · Answer

is this for trying to call a suspend function in shared folder from a aync function in Swift

Howie Nguyen · Answer

Because I am also having this problem

ephemient · Answer

no you have a different problem

ursus · Answer

I see so possibly in future

ursus · Answer

wondering about some generic thing but that would require a suspending lambda so only concrete wrappers i e codegen to the rescue

ursus · Answer

but the adapter will live in kotlin so its fine lmao the rubberducking sorry smile

ursus · Answer

```class SuspendAdapter lt T gt private val scope = CoroutineScope Dispatchers Default + SupervisorJob fun adapt action suspend gt R onNext gt R CancellationHandle val job = scope launch val result = action onNext result return CancellationHandle job ``` nevermind you d need a concrete FooAdapter class anyways to wrap Foo api so yea codegen to generate them

ursus · Answer

thanks

ephemient · Answer

hmm seems my previous proposal sorta exists in some form although it uses one common scope instead of creating one per swift operation as I d have chosen <https github com rickclephas KMP NativeCoroutines blob master KMPNativeCoroutinesAsync AsyncFunction swift>