On 20 April 2017 at 17:03, Igor Mironchik <igor.mironc...@gmail.com> wrote: > Hi, > > > 20.04.2017 7:52, Ch'Gans пишет: >> >> On 20 April 2017 at 16:38, Igor Mironchik <igor.mironc...@gmail.com> >> wrote: >>> >>> Hi, >>> >>> What the benefits of qobject_cast<> on simple static_cast<>? Or there is >>> no >> >> qobject_cast >> - works only on QObject (obviously) >> - returns nullptr if the object cannot be casted to the required type > > > And it can fail if QObject derived pointer was returned from plugin.
Is this a statement or a question? if I'm not wrong, qobject_cast relies on QMetaObject (object->metaObject() and Class::staticMetaObject()). Actually, i've just checked the sources and qobject_cast<T*>(object) returns "static_cast<T*>(T::staticMetaObject().cast(object))" and QMetaObject::cast(obj) returns "(obj && obj->metaObject()->inherits(this)) ? obj : nullptr" QMetaObject allows you to walk the class inheritance hierarchy, and inherits() does exactly this. I don't think that the fact that the object comes from a plugin can make inherits() fail. If you are able to load the plugin successfully, it means that you have no unresolved symbols. AFAIK, the only problems with plugins is meta-type registration that has to be done explicitly by calling qRegisterMataType(...); I don't think that QMetaObject suffers from this. Maybe someone can confirm this. > >> - doesn't relies on RTTI, and is way faster than dynamic cast > > > This is understandable. But with comparison with static cast there are no > benefits? My point was: dynamic_cast is safer than static_cast, and qobject_cast is faster than dynamic_cast. So qobject_cast is a "double win" over static_cast and dynamic_cast. Chris > > >> >> Chris >> >>> one? >>> >>> _______________________________________________ >>> Interest mailing list >>> Interest@qt-project.org >>> http://lists.qt-project.org/mailman/listinfo/interest > > _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
