How can I convert `List<T>` (where `T` is a `CStructVar`) to `CValuesRef<T>`?

# kotlin-native

[Adam S]

How can I convert List<T> (where T is a CStructVar) to CValuesRef<T>?

[Adam S]

list2cvalues.kt

list2cvalues.kt

[Oleg Yukhnevich]

what is the points type in C?

[Adam S]

the C function signature is

void GeneratedExternalFunction(Vector2 *points)

[Adam S]

and Vector2 is

typedef struct Vector2 {
    float x;
    float y;
} Vector2;

[Adam S]

Kotlin generates these types:

public external expect fun GeneratedExternalFunction
(points: kotlinx.cinterop.CValuesRef<cinterop.Vector2>?): kotlin.Unit { /* compiled code */ }

public final expect class Vector2 public constructor(rawPtr: kotlinx.cinterop.NativePtr /* = kotlin.native.internal.NativePtr */) : kotlinx.cinterop.CStructVar {
    public expect companion object : kotlinx.cinterop.CStructVar.Type {
    }

    public expect final var x: kotlin.Float /* compiled code */

    public expect final var y: kotlin.Float /* compiled code */
}

[Oleg Yukhnevich]

you will need to do smth like this:

val vectorValues: List<CValue<Vector2>> = vectors.map { it.readValue() }
val array = allocArray<T>(elements.size)
vectorValues.forEachIndexed { index, element -> element.place(array.get(index).ptr) }
GeneratedExternalFunction(array)

[Oleg Yukhnevich]

for context: https://youtrack.jetbrains.com/issue/KT-56570/CInterop-Improve-experience-when-working-with-arrays-of-structs

[Adam S]

thanks! This seems to compile

array2values.kt

[Adam S]

I did a bit of refactoring, do you think this helper function works the same?

inline fun <reified T : CStructVar> NativePlacement.allocArrayOfStructs(
  values: List<T>,
): CPointer<T> = allocArray(values.size) { index ->
  values[index].readValue().place(ptr)
}

[Oleg Yukhnevich]

yeah, looks like