From <https://kotlinlang.org/docs/tutorials/native...

# kotlin-native

[magnumrocha]

From https://kotlinlang.org/docs/tutorials/native/mapping-function-pointers-from-c.html:
"We use the staticCFunction{..} helper function from Kotlin/Native to wrap a Kotlin lambda function into a C function pointer. It only allows having unbound and non-capturing lambda functions. For example, it is not able to use a local variable from the function. We may only use globally visible declarations."

"globally visible declarations" -> how can access my global kotlin declarations inside the the lambda of staticCFunction , because I have tested some approaches and only could have access to functions that use kotlin global functions (like println ), if I use some of my global scoped declarations my code fails on kotlin native call stack...

[Dominaezzz]

Does the C-api not offer some sort of userPtr ?

[magnumrocha]

yes, I have a pointer and I am using it, but the pointer is for a Kotlin class that contains a ConflatedBroadcastChannel as a member, and every time I do:

userPtr.asStableRef<MyKClass>().get().broadcaster.offer(Unit)

I have EXC_BAD_ACCESS in my Swift Code on iOS side...

[magnumrocha]

I know that probably the C function is running in another thread and I am trying to calling something from my kotlin code... but I've tried to call the code using:

dispatch_async(dispatch_get_main_queue()) {...}

and the problem still happens

[Dominaezzz]

In that case, you should use the pointer to make a wrapper function that can take a capturing lambda. (You can then capture the channel and other things)

[magnumrocha]

I'm sorry, how can I "use the pointer to make a wrapper function"?

[Dominaezzz]

What is the signature of your function? (It would be easier to show you)

[magnumrocha]

so, I have:

class MyKClass {
    val broadcast = ConflatedBroadcastChannel<Unit>()

    val selfPtr: StableRef<MyKClass>
    
    init {
        selfPtr = StableRef.create(this)

        val callback: SomeCallbackClass = staticCFunction { value: SomeClassType, info: COpaquePointer? ->
            if (info == null) { return@staticCFunction }
            info.asStableRef<MyKClass>().get().broadcast.offer(Unit) // here causes EXC_BAD_ACCESS!
        }
        
        someNativeApi(selftPtr.asCPointer(), callback)
    }
}

[magnumrocha]

that's my use case...

[Dominaezzz]

class MyKClass {
    val broadcast = ConflatedBroadcastChannel<Unit>()
    
    init {
        someNativeApiWrapper() { value: SomeClassType ->
            broadcast.offer(Unit) // here causes EXC_BAD_ACCESS!
        }
    }
    
    fun someNativeApiWrapper(callback: (value: SomeClassType) -> Unit) {
        val callbackPtr = StableRef.create(callback)
        someNativeApi(callbackPtr.asCPointer(), staticCFunction { value: SomeClassType, info: COpaquePointer? ->
            if (info == null) { return@staticCFunction }
            val realCallbackPtr = info.asStableRef<(SomeClassType) -> Unit>().get()
            realCallbackPtr(value)
            // Might free StableRef here
        })
    }
}