《Effective C++》 Item 35

This basic design — having clients call private virtual functions indirectly through public non-virtual member functions — is known as the non-virtual interface (NVI) idiom

 

class GameCharacter {

public:
  int healthValue() const // derived classes do not redefine
  { // this — see Item 36
    ... // do "before" stuff — see below
    int retVal = doHealthValue(); // do the real work
    ... // do "after" stuff — see below
    return retVal;
  }
  ...
private:
  virtual int doHealthValue() const // derived classes may redefine this
  {
   ... // default algorithm for calculating
  } // character's health
};


 

we replace the use of a function pointer (such as healthFunc) with an object of type TR1::function. As explains, such objects may hold any callable entity (i.e., function pointer, function object, or member function pointer) whose signature is compatible with what is expected.

 

int defaultHealthCalc(const GameCharacter& gc); // as before

typedef std::tr1::function<int (const GameCharacter&)> HealthCalcFunc;