策略模式

策略模式最大的特点在于其低耦合性。在具体的实现中采用不同的算法，不会影响到调用者。其基本组成包括：抽象策略角色、具体策略角色和环境角色。

下面是以C++实现的示例代码：

#include <iostream>
using namespace std;

class IStrategy{
public:
    IStrategy() {}
    virtual ~IStrategy() {}
    virtual void Operate() = 0; // pure virtual function
};

class Context
{
public:
    Context(IStrategy *p)
    {
        m_p = p;
    }

    ~Context() 
    {
        delete m_p;
    }

    void Operate()
    {
        m_p->Operate();
    }

private:
    IStrategy *m_p;
};

class BackDoor : public IStrategy
{
public:
    BackDoor() {}
    virtual ~BackDoor() {}

    virtual void Operate()
    {
        cout << "找乔国老帮忙，让吴国太给孙权施加压力。" << endl;
    }
};

class GivenGreenLight : public IStrategy
{
public:
    GivenGreenLight() {}
    virtual ~GivenGreenLight() {}

    virtual void Operate()
    {
        cout << "求吴国太开个绿灯，放行！" << endl;
    }
};

class BlockEnemy : public IStrategy
{
public:
    BlockEnemy() {}
    virtual ~BlockEnemy() {}

    virtual void Operate()
    {
        cout << "孙夫人断后，挡住追兵。" << endl;
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    Context *pContext;

    cout << "----------刚刚到吴国的时候拆第一个----------" << endl;
    pContext = new Context(new BackDoor());
    pContext->Operate();
    delete pContext;

    cout << "\n\n\n" << endl;
    cout << "----------刘备乐不思蜀了，拆第二个了----------" << endl;
    pContext = new Context(new GivenGreenLight());
    pContext->Operate();
    delete pContext;

    cout << "\n\n\n" << endl;
    cout << "----------孙权的小兵追了，咋办？拆第三个----------" << endl;
    pContext = new Context(new BlockEnemy());
    pContext->Operate();
    delete pContext;

    return 0;
}

本文参考了CBF4LIFE写的设计模式。