The Resizer virtual functor is useless without a virtual destructor.

[KubaO]

The Resizer implements a virtual functor. As such, it must include a virtual destructor. In C++11 code, instead of a Resizer one should use std::function<void(QGraphicsItem*,const QRectF&)>.

[graeioume]

Adding the destructor / ~Resizer() {} / as recommended squelched a number of warnings I was receiving about unused parameters caused by overloaded functions.