Why is QWidget's destructor not virtual?

Looking at qwidget.h, I found the destructor as below:

~QWidget();

I was wondering why this is not开发者_如何学运维 declared as virtual

The destructor is virtual, because QWidget derives from QObject which does have a virtual destructor. Why it's not declared virtual in the code is a either style issue or a harmless mistake. I would have declared it virtual myself.