fun with NativeCall callbacks

gistfile1.txt

      # should be size_t
      my sub ca8_mal(int) returns CArray[int8]
          is native
          is symbol('malloc') { * };
      my sub ca8_free(CArray[int8])
          is native
          is symbol('free') { * };

      # int should be size_t
      my sub end_m(Instance, &callback (int --> CArray[int8]))
          returns CArray[int8]
          is native('libmhash')
          is symbol('mhash_end_m') { * };

      method finalize() {
          my $sizeof; # try to capture the malloc size using the end_m cb
          my $c := end_m(self, sub (int $s) { say "<<$s>>"; $sizeof = $s; ca8_mal($s) });
          my $res := buf8.new($c[0..^$sizeof].list);
          ca8_free($c);
          $res := buf8.new($res.values.reverse)
              if $swab_4byte_digests and $sizeof == 4;
          $res;
      }