Eric Blake <ebl...@redhat.com> writes:
> On 04/18/2018 11:45 AM, Markus Armbruster wrote:
>
>>> 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"?
>
> It doesn't, but PATCH 4 does:
>
>> /**
>> * qobject_ref(): Increment QObject's reference count
>> + *
>> + * Returns: the same @obj. The type of @obj will be propagated to the
>> + * return type.
>> */
>> -#define qobject_ref(obj) qobject_ref_impl(QOBJECT(obj))
>> +#define qobject_ref(obj) ((typeof(obj)) qobject_ref_impl(QOBJECT(obj)))
Easy enough to fix:
#define qobject_ref(obj) ({ \
typeof(obj) _obj = obj; \
qobject_ref_impl(QOBJECT(_obj)); \
_obj; \
})
Look ma, no type casts!
