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

时间：2011-04-02 来源：Ray Z

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.