有一部分人总是主张virtual函数几乎总应该是private:例如下面这个例子，例子时候游戏，游戏里面的任务都拥有健康值这一属性：
class GameCharacter{ public: int healthValue()const{ ... int retVal = doHealthValue(); ... return retVal; } private: virtual int doHealthValue() const { }//上面的这个non-virtual函数实际上是virtual函数的一个外覆器 };
1 class GameCharacter; 2 int defaultHealthCalc(const GameCharacter & gc); 3 class GameCharacter{ 4 public: 5 typedef std::function<int (const GameCharacter & )> HealCalcFunc 6 explicit GameCharacter(HealCalcFunc hcf = defaultHealthCalc) 7 :healthFunc(hcf){} 8 int healthValue() const 9 {return healthFunc(* this); } 10 ... 11 private: 12 HealCalcFunc healthFunc; 13 };
实际上，这个typedef带来的弹性是很大的：
1 short clacHealth(const GameCharacter &); 2 //或者是一个函数对象 3 struct HealCalculater{ 4 public: 5 float operator()(const GameCharacters & gc) const ; 6 }; 7 //或者是一个成员函数。 8 class GameLevel{ 9 public: 10 float Health(const GameCharacters)const; 11 }; 12 GameCharacters character1(clacHealth); 13 GameCharacters character2(HealCalculater()); 14 GameLevel levelObj; 15 GameCharacters character3(std::bind(&GameLevel::health, levelObj, _1));//不记得这样写对不对，待查
1 class HealCalculater; 2 class GameCharacter; 3 int defaultHealthCalc(const GameCharacter & gc); 4 class GameCharacter{ 5 public: 6 typedef std::function<int (const GameCharacter & )> HealCalcFunc 7 explicit GameCharacter(HealCalcFunc hcf = defaultHealthCalc) 8 :healthFunc(hcf){} 9 int healthValue() const 10 {return healthFunc(* this); } 11 ... 12 private: 13 HealCalcFunc * phealthFunc; 14 }; 15 HealCalculater{ 16 public : 17 virtual int calc(const GameCharacter & gc)const 18 {} //也可以只声明一个接口 19 }
原文：http://www.cnblogs.com/-wang-cheng/p/4889778.html