条款31 让函数根据一个以上的对象类型来决定如何虚化

普通函数重载

#include<iostream>using namespace std;class SpaceShip;class SpaceStation;class Asteriod;class GameObject{      public:};class SpaceShip: public GameObject{      public:};class SpaceStation: public GameObject{      public:};class Asteriod: public GameObject{      public:};void collide(GameObject &ob1,GameObject &ob2){     cout<<"GameObject &ob1=>GameObject &ob2"<<endl;}void collide(GameObject& ob1,SpaceShip& ob2){     cout<<"GameObject &ob1=>SpaceShip &ob2"<<endl;}void collide(SpaceStation& ob1,Asteriod& ob2){     cout<<"SpaceStation &ob1=>Asteriod &ob2"<<endl;}void collide(SpaceShip &ob1,SpaceStation &ob2){     cout<<"SpaceShip &ob1=>SpaceStation &ob2"<<endl;}void TestCollide(GameObject &ob1,GameObject &ob2){     collide(ob1,ob2);}int main(){    SpaceShip sp;    SpaceStation ss;    TestCollide(sp,ss);//对象切片     cout<<"==============================="<<endl;    collide(sp,ss);//调用重载函数     getchar();    return 0;}

结果：

条款31所述方法实现多态

#include<iostream>using namespace std;class SpaceShip;class SpaceStation;class Asteriod;class GameObject{      public:       virtual void collide(GameObject& otherObject) = 0;       virtual void collide(SpaceShip& otherObject) = 0;       virtual void collide(SpaceStation& otherObject) = 0;       virtual void collide(Asteriod& otherObject) = 0;};void GameObject::collide(GameObject& otherObject){     cout<<"Base::collide"<<endl;}class SpaceShip: public GameObject{      public:      virtual void collide(GameObject& otherObject)      {              cout<<"SpaceShip::collide"<<endl;              otherObject.collide(*this);      }      virtual void collide(SpaceShip& otherObject)      {              cout<<"SpaceShip::collide(SpaceShip& otherObject)"<<endl;      }      virtual void collide(SpaceStation& otherObject)      {              cout<<"SpaceShip::collide(SpaceStation& otherObject)"<<endl;      }      virtual void collide(Asteriod& otherObject)      {              cout<<"SpaceShip::collide(Asteriod& otherObject)"<<endl;      }};class SpaceStation: public GameObject{      public:      virtual void collide(GameObject& otherObject)      {              cout<<"SpaceStation::collide"<<endl;              otherObject.collide(*this);      }      virtual void collide(SpaceShip& otherObject)      {              cout<<"SpaceStation::collide(SpaceShip& otherObject)"<<endl;      }      virtual void collide(SpaceStation& otherObject)      {              cout<<"SpaceStation::collide(SpaceStation& otherObject)"<<endl;      }      virtual void collide(Asteriod& otherObject)      {              cout<<"SpaceStation::collide(Asteriod& otherObject)"<<endl;      }};class Asteriod: public GameObject{      public:      virtual void collide(GameObject& otherObject)      {              cout<<"Asteriod::collide"<<endl;              otherObject.collide(*this);      }      virtual void collide(SpaceShip& otherObject)      {              cout<<"Asteriod::collide(SpaceShip& otherObject)"<<endl;      }      virtual void collide(SpaceStation& otherObject)      {              cout<<"Asteriod::collide(SpaceStation& otherObject)"<<endl;      }      virtual void collide(Asteriod& otherObject)      {              cout<<"Asteriod::collide(Asteriod& otherObject)"<<endl;      }};void TestCollide(GameObject &ob1,GameObject &ob2){    ob1.collide(ob2);}int main(){    SpaceShip oShip;    SpaceStation oStation;    Asteriod oAst;    GameObject& g1=oShip;    GameObject& g2=oStation;    GameObject& g3=oAst;TestCollide(g1,g1);cout<<"==============================="<<endl;TestCollide(g1,g2);cout<<"==============================="<<endl;TestCollide(g1,g3);cout<<"==============================="<<endl;TestCollide(g2,g3);    getchar();    return 0;}

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