what is the idea around handling objc checked exce...

# kotlin-native

[Michal Klimczak]

what is the idea around handling objc checked exceptions in kotlin native (docs only really mention the opposite situation. E.g. consider AVAudioPlayer, in swift you deal with it like that:

do {
    try AVAudioPlayer(contentsOf: url)
} catch {
    // handle exception
}

In Kotlin Native it's signature is

public constructor(contentsOfURL: platform.Foundation.NSURL, error: CPointer<ObjCObjectVar<NSError?>>?)

How do you handle error here?

[Sam]

Objc makes a distinction between errors and exceptions. Errors are recoverable events whereas exceptions are not. An ObjC exception is thrown and you should only do a little cleanup before exiting the app.

[Michal Klimczak]

Okay, but given the signature of the function above, how do I handle this recoverable error? There's something passed as an argument to the function and it references a potential error when it's thrown, I assume. Right now I just pass null there. What's the right way to handle it?

[Sam]

You need to pass a pointer into the function. Wrap it in a memscoped block so that it is automatically reclaimed. Something like this should work.

val player: AVAudioPlayer
memScoped {
    val errorPtr: ObjCObjectVar<NSError?> = alloc<ObjCObjectVar<NSError?>>()
    player = AVAudioPlayer(url, errorPtr.ptr)
    println(errorPtr.value) //Will be null if the call succeeds.
}

[Michal Klimczak]

Thank you! Do you maybe know a good source of knowledge for this low level memory handling stuff in kotlin native? It's probably easier if you come from C workd

[Sam]

Only what comes out of the docs. Some of the example code in the K/N repo is helpful too.