Hi guys, I have a question regarding `Object pinn...

# kotlin-native

[Vlad Balan]

Hi guys,

I have a question regarding Object pinning.
According to the documentation this can be done as follows:

fun readData(fd: Int): String {
  val buffer = ByteArray(1024)
  buffer.usePinned { pinned ->
    while (true) {
      val length = recv(fd, pinned.addressOf(0), buffer.size.convert(), 0).toInt()
      if (length <= 0) {
        break
     }
     // Now `buffer` has raw data obtained from the `recv()` call.
   }
 }
}

What about if I want to use it on something else than a buffer. For example on cValue<cairo_text_extents_t> where cairo_text_extents_t is:

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

    public final var height: kotlin.Double /* compiled code */

    public final var width: kotlin.Double /* compiled code */

    public final var x_advance: kotlin.Double /* compiled code */

    public final var x_bearing: kotlin.Double /* compiled code */

    public final var y_advance: kotlin.Double /* compiled code */

    public final var y_bearing: kotlin.Double /* compiled code */
}

and the function to which I want to provide it is:

@kotlinx.cinterop.internal.CCall public external fun cairo_glyph_extents(cr: kotlinx.cinterop.CValuesRef<libcairo.cairo_t /* = cnames.structs._cairo */>?, glyphs: kotlinx.cinterop.CValuesRef<libcairo.cairo_glyph_t>?, num_glyphs: <http://kotlin.Int|kotlin.Int>, extents: kotlinx.cinterop.CValuesRef<libcairo.cairo_text_extents_t>?): kotlin.Unit { /* compiled code */ }

My problem is that cValue<cairo_text_extents_t> does not have the function addressOf .
I provide a small code snippet to show what I mean:

val glyph = cValue<cairo_glyph_t>()
val extents = cValue<cairo_text_extents_t>()
extents.usePinned {pinned ->
	memScoped {
		cairo_glyph_extents(context.cairo, glyph.ptr, 1, pinned.<what>) // how to get the address 
	}
}

Does anybody know how I can do this?

Thanks in advance!

[Dominaezzz]

In the case of structs, you don't/can't pin them. Pinning is fairly limited.
The values returned by cValue are considered immutable, so you won't be able to mutate it like that.

[Dominaezzz]

You can achieve what you want by either using the copy function or using cValue<cairo_text_extents_t> { // mutate here } to mutate it at initialisation time.

[Vlad Balan]

Thanks!