Item 35: Consider alternatives to virtual functions(Effective C++)

The fundamental advice of this Item is to consider alternatives to virtual functions when searching for a design for the problem you're trying to solve. Here's a quick recap the alternatives we examined:

• Use the non-virtual interface idiom (NVI idiom), a form of the Template Method design pattern that wraps public non-virtual member functions around less accessible virtual functions.

• Replace virtual functions with function pointer data members, a stripped-down manifestation of the Strategy design pattern.

• Replace virtual functions with tr1::function data members, thus allowing use of any callable entity with a signature compatible with what you need. This, too, is a form of the Strategy design pattern.

• Replace virtual functions in one hierarchy with virtual functions in another hierarchy. This is the conventional implementation of the Strategy design pattern.

• Alternatives to virtual functions include the NVI idiom and various forms of the Strategy design pattern. The NVI idiom is itself an example of the Template Method design pattern.

• A disadvantage of moving functionality from a member function to a function outside the class is that the non-member function lacks access to the class's non-public members.

• tr1::function objects act like generalized function pointers. Such objects support all callable entities compatible with a given target signature.