test.c

#include <stdio.h>
#include <stdlib.h>

struct foo {
    int x;
};

void foo_init(struct foo **f) {
    *f = malloc(sizeof(struct foo));
    printf("malloc'd, pointer = %p\n", (void *) *f);
}

void foo_shutdown(struct foo *f) {
    printf("freeing, pointer = %p\n", (void *) f);
    free(f);
}

void foo_test() { printf("foo\n"); }

test.pl6

use NativeCall;

class foo is repr('CPointer') { }

sub foo_init(Pointer[foo])
    is native('test')
    { * }

sub foo_shutdown(foo)
    is native('test')
    { * }

sub foo_test()
    is native('test')
    { * }

# foo_test();   # works

my Pointer[foo] $p = Pointer[foo].new;
foo_init($p);
say $p.deref();             # how do I get my pointer back to pass to foo_shutdown?

#foo_shutdown($p.deref());