Good day! In the book C++ GUI Programming with Qt 4 (2nd Edition) there's not much information about QMetaType and the Qt's internal subsystem. There's the statement at qRegisterMetaType<http://qt-project.org/doc/qt-5.0/qtcore/qmetatype.html#qRegisterMetaType> which says "...After a type has been registered, you can create and destroy objects of that type dynamically at run-time. To use the type T in QVariant<http://qt-project.org/doc/qt-5.0/qtcore/qvariant.html>, using Q_DECLARE_METATYPE<http://qt-project.org/doc/qt-5.0/qtcore/qmetatype.html#Q_DECLARE_METATYPE>() is sufficient. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established...." . After reading qmetatype.cpp and qmetatype.h everything Q_DECLARE_METATYPE does is specialization of QMetaTypeId template structure. QVariant inside the static function compare in qvariant.cpp uses QMetaType::IsRegistered method which in fact checks if the type was registered in customTypes using either qRegisterMetaType or QMetaTypeId<T>::qt_metatype_id() after Q_DECLARE_METATYPE. Why is it sufficient then to use Q_DECLARE_METATYPE for any template using the declared type? qRegisterMetaType only puts the type to be registered into customTypes vector registering constructor and destructor for the type with an ID (optionally an user may register operator>> and operator<< for the type). Why is it needed to use queued signal and slot connections and QObject::property() API? Furthermore, Q_OBJECT is required for a type using slots/signals. QObject does not meet CopyConstructible requirement for using either Q_DECLARE_METATYPE or qRegisterMetaType.
I'd like to ask you to clearify this. Thank you.
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