Chapter 9

      // push key and value

      XPUSHs(sv_2mortal(newSVpvn(key, len)));

      XPUSHs(sv_mortalcopy(value));

    }

    // free hv explicitly

    SvREFCNT_dec((SV *)hv);

    // return two SVs for each key in the hash

    XSRETURN(count * 2);

  }

  // G_SCALAR or G_VOID context   return a reference to the new hash

  XPUSHs(sv_2mortal(newRV_noinc((SV *)hv)));

The first change in the XSUB is in the return value. By using PPCODE instead of 

CODE, the XSUB is responsible for managing the return stack. As a result, the return 

type is set to void so that xsubpp knows not to provide RETVAL:

void

type_data(type)

  const gchar * type

After that, aside from using PPCODE instead of CODE, the function begins much like 

the XSUB in Listing 9 7. The first new statement is as follows:

  // free keys GList

  g_list_free(keys);

This line used to live in the CLEANUP block, but PPCODE blocks cannot have CLEANUP

blocks, so the call to g_list_free() is moved into the main code body.

The next section uses a new macro, GIMME_V, to examine the context of the 

current call. GIMME_V is the XS author's version of Perl's wantarray built in. It can 

return three possible values G_ARRAY,

3

G_SCALAR, and G_VOID. In this case, I test for 

list context:

  // test context with GIMME_V

  if (GIMME_V == G_ARRAY) {

If you're in list context, the code iterates through the hash and pushes key/value 

pairs onto the return stack. The hash iteration code should look familiar from the 

3. Which probably should be G_LIST since there's no such thing as  array context! 

230