Hey, is it supported (or does it make sense) to have `@Throws` annotation at methods in an interface...

# multiplatform

[krzysztof]

Hey, is it supported (or does it make sense) to have @Throws annotation at methods in an interface, to be implemented in iOS side? Having interface like this:

interface ExampleInterface {
  @Throws(Exception::class)
  fun doIt(): Boolean
}

And using implementing it on Swift side as:

func doIt() throws -> Bool {
  // ...
}

gives an error :

Throwing method cannot be an implementation of an @objc requirement because it returns a value of type 'Bool'; return 'Void' or a type that bridges to an Objective-C class

[François]

It seems it's not working, just found a (dirty) workaround.

interface ExampleInterface {
    @Throws(Exception::class)
    suspend fun doIt(): Boolean
}

class DummyTest: ExampleInterface {
    func doIt() async throws -> KotlinBoolean {
        return true
    }
    
}

[François]

But I'm not brave enough to find the real reason of the issue of interrop between Swift<->Obj-C 😭

[krzysztof]

This gives me an error that the class does not conform to the protocol (it treats doIt as overload), so that not working for me. Which Kotlin version you use?

[François]

I'm using the version Kotin > 2.0.0

[Michael Krussel]

Checkout the function declaration in the Objective-C header, that may give clues on how to implement it in Swift.

[François]

We can only follow what Swift give us from the obj-c declaration, and it's seem incompatible with it.

[krzysztof]

Seems like this is a LLVM issue, where generated header gives mutually exclusive errors
https://github.com/llvm/llvm-project/issues/60024

[François]

if it's really the case, this issue is from last January and no update...

[krzysztof]

I guess no @Throws annotated methods for now. I put together an issue in YT, just to make sure my suspicion is correct