Eric Blake <ebl...@redhat.com> writes: > On 04/17/2018 08:35 AM, Marc-André Lureau wrote: >> All QObject types have the base QObject as first field. This allows to > > s/as/as their/ > >> simplify qobject_to() and will allow further simplification in > > s/allows to simplify/allows the simplification of/ > s/in/in the/ > >> following patch. > > Might also be worth mentioning that this explicitly guarantees that > existing casts work correctly (even though we'd prefer to get rid of > such casts in any location except the qobject.h macros); Markus pointed out: > >>> Uh, there's another reason: existing type casts from QObject * to >>> subtypes. I just spotted one in tests/check-qdict.c: >>> >>> dst = (QDict *)qdict_crumple(src, &error_abort);
As far as I'm concerned, that's the real reason. The simplification plus the check to make it safe seems like a wash. The cast I spotted appears to be the only one, though: $ git-grep '(Q[A-Z][a-z]* \*)' hmp.c: qmp_device_add((QDict *)qdict, NULL, &err); include/qapi/qmp/qobject.h: return (QObject *)obj; qobject/qobject.c:static void (*qdestroy[QTYPE__MAX])(QObject *) = { tests/check-qdict.c: dst = (QDict *)qdict_crumple(src, &error_abort); The first two cast away const, the third isn't a type cast. The fourth one should use qobject_to() instead, regardless of this patch. Do we want to force base to come first anyway? Where does PATCH 2 exploit "base first"? [...]