Casting from QList<InheritedFromQObject> to QList<QObject>

[Kofr]

Hi guys,
I have a problem when casting:

/home/kofr/dev/shit/Converter/converter.cpp:98:

error: invalid static_cast from type 'QList<Unit*>*' to type 'QList<QObject*>* ' 

sourceUnitDataModel = static_cast<QList<QObject *> *>((&modelsByCategory[category]));
                                                                                     

Class Unit is the inherited from QObject class. What might be a problem?

[Chris Kawa]

You can't cast any container<A> to container<B>. Template class types are unrelated, even if T in them has something in common. There might be specializations, some sizes may differ, alignment may vary or buncha other things. Yours is just a special case but these types are just not compatible in general. For compiler it's basically the same as converting vector<int> to vector<string>.

The correct way to do what you want is to create another container and copy the elements casting them one at a time, e.g. using std::transform.

[Kofr]

@Chris-Kawa thx.
I actually cast pointers to containers. does this fact make any difference??

[Chris Kawa]

The two list types are unrelated so casting pointers to them is still not ok at all. To push the previous analogy - for compiler it's like casting int* to string*. You can of course use reinterpret_cast and the compiler will be happy to trust you, but that is in no way correct and will obviously explode in your face at runtime.