Hands-On Design Patterns with C++

A note about destructors

The entire discussion of the NVI is an elaboration on a simple guideline—make virtual functions private (or protected), and present the public interface through non-virtual base class functions. This sounds fine until it runs head-on into another well-known guideline—if the class has at least one virtual function, its destructor must also be made virtual. Since the two are in conflict, some clarification is needed.

The reason to make destructors virtual is this—if the object is deleted polymorphically, for example, a derived class object is deleted through a pointer to the base class, the destructor must be virtual, otherwise only the base part of the class will be destructed (the usual result is slicing of the class, ...