Is it possible to catch kotlin exception in swift ...

# kotlin-native

[Jaroslav]

Is it possible to catch kotlin exception in swift code? (kotlin part imported as a framework)

[thevery]

Yes if cheched

[Jaroslav]

And there is a little complication:

suspend fun <T : Any> call(command: Command<T>): T{
// here exception can be thrown
}

fun <T : Any> callAsync(command: Command<T>, context: CoroutineContext): Deferred<T> {
        return GlobalScope.async(context) {
            call(command = command)
        }
    }

ios runs callAsync, while exception is thrown inside suspend function

[thevery]

You need @Throws annotation to make it work

[Jaroslav]

where? idea doesn’t recognize it 🙂

[Jaroslav]

Unresolved reverence Throws

[olonho]

https://github.com/JetBrains/kotlin-native/blob/c1a41c9dc4c69d008da0c5a83ace00f63b84dec4/runtime/src/main/kotlin/kotlin/native/Annotations.kt#L41

[Jaroslav]

hmm.. ok, that compiled, thanks!

[Jaroslav]

But IntelliJ doesn’t recognize it

[olonho]

Maybe you have incorrect build script or due to bug your code is not recognized as native module. Can you use other pure native APIs?

[svyatoslav.scherbina]

Kotlin/Native @Throws annotation can’t be imported to common code. Instead you can declare it as expect annotation class with actual typealias.

[Konstantin Petrukhnov]

@svyatoslav.scherbina any code example?

[Jaroslav]

OK, I’ve added @Throws, now objc method has error param and in swift I can use try/catch. But, as actual exception is thrown asynchronously somewhere in the depths of Deferred, it isn’t catched

[Jaroslav]

I’ve now added invokeOnCompletion(onCancelling: which receives thrown error, but app crashes nonetheless with the same error

[svyatoslav.scherbina]

@Konstantin Petrukhnov

// Common code:
@Target(AnnotationTarget.FUNCTION, AnnotationTarget.CONSTRUCTOR)
expect annotation class Throws(vararg val exceptionClasses: kotlin.reflect.KClass<out kotlin.Throwable>)

// Android code:
actual typealias Throws = kotlin.jvm.Throws

// iOS code:
actual typealias Throws = kotlin.native.Throws

[svyatoslav.scherbina]

@Jaroslav

I’ve now added invokeOnCompletion(onCancelling: which receives thrown error, but app crashes nonetheless with the same error

Which one?

[Jaroslav]

ios app

[svyatoslav.scherbina]

Which error?

[Jaroslav]

suspend function throws an exception, then on ios part my callback that was given via invokeOnCompletion(onCancelling: get’s called, printing error shows that’s the same one that was thrown, for now everything’s ok, but then after that callback is executed, app crashes with Uncaught Kotlin exception:. Setting NSSetUncaughtExceptionHandler doesn’t help either.

[Jaroslav]

and crashes with the same error that was printed inside invokeOnCompletion(onCancelling:

[svyatoslav.scherbina]

Could you please provide exception and crash stacktraces? A sample to reproduce the issue would also be useful.

[Jaroslav]

ok, I’ll try to make a demo app later today

[Jaroslav]

check this out: https://github.com/jaroslavas/kotlin-mpp-example

[svyatoslav.scherbina]

@Throws

suspend fun anotherGreeting(): String {

This is wrong.
@Throws annotation must be applied to the function that is called from Swift directly.

[Jaroslav]

I’ll ad that in a minute, but I’ve tried that before - it won’t help

[Jaroslav]

yes, that didn’t help: https://github.com/jaroslavas/kotlin-mpp-example/commit/e1671cb53aa8deba2c33e9f576bd6b787bc30f1a

[svyatoslav.scherbina]

Yes, because @Throws annotation must be added to the function that is called from Swift and throws an exception.
In your case this function seems to be deferred.getCompleted().

[Jaroslav]

yeah, but deferred is an interface, so even if I override it with mine, globalScope.async will still return original interface that has no @throws

[svyatoslav.scherbina]

Yes, that’s why it is required to add @Throws wrapper for deferred.getCompleted().

[Jaroslav]

sorry, maybe I’m too green in kotlin, but how this can be done?

[svyatoslav.scherbina]

@Throws
fun <T> getCompletedOrThrow(deferred: Deferred<T>): T = deferred.getCompleted()

[Jaroslav]

thanks! I think I’ve got that, finally 🙂

[Jaroslav]

if someone’s interested, here is the code: https://github.com/jaroslavas/kotlin-mpp-example/commit/9f1023775ce4677cc344ab2d80c517bab6eea8ca

[aakira]

Do you have any ideas about js?

https://kotlinlang.slack.com/archives/C3SGXARS6/p1541663221249900?thread_ts=1541595589.233800&cid=C3SGXARS6

[svyatoslav.scherbina]

You can either apply @OptionalExpectation (https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-optional-expectation/index.html) or declare a dummy actual annotation class Throws for JS.

[aakira]

Nice annotation!
Thank you so much 😄