Hi, is there a way to wrap `staticCFunction` call?...

# kotlin-native

[Tadeas Kriz]

Hi, is there a way to wrap staticCFunction call? I'm trying to declare expect fun <R> staticCFunction(function: () -> R): CPointer<CFunction<() -> R>> in commonMain, but when I try to declare actual fun <R> staticCFunction(function: () -> R): CPointer<CFunction<() -> R>> = kotlinx.cinterop.staticCFunction(function) in iosMain, I'm getting kotlinx.cinterop.staticCFunction must take an unbound, non-capturing function or lambda error. I tried putting in the internal annotations @VolatileLambda on function and @TypedIntrinsic(IntrinsicType.INTEROP_STATIC_C_FUNCTION) on the actual fun staticCFunction but it didn't help.

Is there anything I could do to make this work?

[ephemient]

does it work without `expect`/`actual`? the restrictions on staticCFunction are strict because it really needs to be static at build time, it can't create a closure there

[Tadeas Kriz]

Yeah, sorry I forgot to mention that without expect/actual it also doesn't work

[Tadeas Kriz]

I also tried declaring it as inline fun so that it'd actually be using staticCFunction directly but that also doesn't work

[Tadeas Kriz]

From looking into the compiler sources, it's happening because it gets expression of type IrGetValueImpl but expects IrFunctionReference or IrFunctionExpression. Which sounds like staticCFunction has to always be called directly and can't be delegated.

[ephemient]

I'm not sure what you mean by delegated but it must always be of the form

staticCFunction(::function)

where function is a static function (e.g. top-level) or equivalent lambda. it may not capture anything because there is a C function pointer cannot hold anything additional

[Tadeas Kriz]

By delegated I mean you can't do:

inline fun callStaticCFunction(noinline function: () -> Unit) {
  staticCFunction(function)
}

even if you call callStaticCFunction(::function) and all the other requirements are met

[Landry Norris]

You can't capture anything in the staticCFunction call. In your case, you're capturing the local variable 'function'. In staticCFunction, you can only pass global variables or references to raw methods (not functional variables).

[Tadeas Kriz]

Yeah, function is global Kotlin function and it works when I call staticCFunction(::function) directly, because of how the backend checker is verifying the IR. I don't really capture anything in my callStaticCFunction, but it'd require the backend checker to do more extensive check which would probably slow down the compile

[Alexander Hinze]

Already opened a ticket regarding this issue
https://youtrack.jetbrains.com/issue/KT-71839/Make-VolatileLambda-public-for-parameters-intended-for-native-function-calls