Hello, I just started using Kotlin/Native and I'm a bit confused with how I can turn a CValue<T&g...

# kotlin-native

[Matthieu Stombellini]

Hello, I just started using Kotlin/Native and I'm a bit confused with how I can turn a CValue<T> into T. I know useContents exist but is there a more practical way of doing this?

val result: CValue<Thing> = my_c_function_call()
val resultButRealThisTime: Thing = ???

Doing

val result = my_c_function_call()
val resultButReal: Thing? = null
result.useContents { resultButReal = this@useContents }

Works, but looks awful and I don't think that's how you're supposed to do that

[russhwolf]

Not totally sure but I think you could do something like

val resultButReal: Thing = result.useContents { this }

[Matthieu Stombellini]

True, that's much simpler, thanks for the tip! I'm still wondering if that wouldn't cause memory-management issues, the description of useContents in the docs seem to say that it allocates memory inside useContents? I'm pretty confused

[Matthieu Stombellini]

Doesn't look like that's working, the allocation is temporary and "escaping" stuff from useContents leads to ugly errors reported by valgrind

[russhwolf]

Does that same issue not happen with your original code?

[mkrussel]

Should happen with both. My guess is both implementations creates undefined behavior.

In general you need to do whatever you need the value for inside the useContents method. If you need to be storing it for later use, store it as a CValue.

[Dominaezzz]

Is Thing a struct? If so, you'll have to allocate with nativeHeap to do what you want here.
Although it's best to leave it inside useContents if you can so garbage collection still works.