Hi, Igor Your example is incorrect, cause you forget about Q_OBJECT macro in Channel class
On Thu, Apr 20, 2017 at 8:56 AM, Igor Mironchik <igor.mironc...@gmail.com> wrote: > > > 20.04.2017 8:47, Ch'Gans пишет: > >> 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. > > > Exactly! qobject_cast<> will fail. > > Look in application you have: > > class Channel > : public QObject > {}; > > In plugin you have: > > class MyChannel > : public Channel > {}; > > Channel * create(); > > In application you call: > > Channel * ch = create(); > > And use this object in your application. > > Then in one slot in application you can have: > > void mySlot() > { > Channel * ch = qobject_cast< Channel* > ( sender() ); > // You are 100% sure that sender() is Channel!!! > // And this cast will fail!!! > > } > >> >> 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 _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest