Ugly hack for assigning Callables to CStruct members in Perl6

NativeCall-hack.txt

C
Native library header (ui.h):
...
struct uiAreaHandler {
  void (*Draw)(uiAreaHandler *, uiArea *, uiAreaDrawParams *);
  #Skipping the rest
}
...

test.c, compiled to libtest.so:
#include "ui.h"
#include <stddef.h>
#Takes a function that has exactly the same signature as the function pointer in the struct
size_t get_pointer_Draw( void (*f)(uiAreaHandler *, uiArea *, uiAreaDrawParams *)) {
  return f;
}

Perl6 NativeCall:
sub get_pointer_Draw( &f (Pointer, Pointer, Pointer) ) returns size_t is native("./test") { * }

#CStruct for native library
#See https://stackoverflow.com/questions/43543217/passing-pointer-to-pointer-in-perl-6-nativecall
class uiAreaHandler is repr('CStruct') {
  has size_t $.Draw; 
  #This is really a Pointer, but Pointer is immutable. 
  #size_t and Pointer are the same size, but size_t is mutable.
 
  submethod BUILD(:$Draw!) {
    $!Draw = get_pointer_Draw($Draw); #$Draw is always a Callable
    #Assign the function pointer (which is masquerading as size_t) to the struct member
    #The native library's C code treats this as a pointer, so the function call works.
  }
}