设计模式

策略模式(strategy pattern)

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定义：策略模式定义了算法族, 将算法分别封装起来，让他们之间可以互相替换，让算法的实现独立于算法的使用者

wiki

In computer programming, the strategy pattern (also known as the policy pattern) is a behavioural software design pattern that enables an algorithm's behavior to be selected at runtime. The strategy pattern

defines a family of algorithms,
encapsulates each algorithm, and
makes the algorithms interchangeable within that family.

原则：

• 找出应用中的变化之处，并封装起来
• 多用组合，少用继承
• 针对接口编程，不针对实例编程

举个栗子:

code:

• 鸭子类，鸭子有会叫真鸭子，还有模型小鸭
• 鸭子主类中，将将飞和叫易变动的属性分割出来，以组合这两个类的方式，定义通用的鸭子

class Duck{

public:
    Duck()
    {

    }

    void performFly()
    {
        m_flyBehavior.fly();
    }

    void performQuack()
    {
        m_quackBehavior.quack();
    }

    void setFlyBehavior(FlyBehavior & fb)
    {
        m_flyBehavior = fb;
    }

    void setQuackBehavior(QuackBehavior & qb)
    {
        m_quackBehavior = qb;
    }

private:
    FlyBehavior m_flyBehavior;
    QuackBehavior m_quackBehavior;
}

• 
  
• 飞的类型
  

one time one thing, 飞行类算法

class FlyBehavior
{
public:
    virtual void fly();
}

class FlyWithWings : public FlyBehavior
{
public:
    virtual void fly()
    {
        std::cout << "我用翅膀灰" << std::endl;
    }
}

class FlyNoWay : public FlyBehavior
{
public:
    virtual void fly()
    {
        std::cout << "飞毛线，灰不起来" << std::endl;
    }
}

• 嘎嘎叫的类

class QuackBehavior
{
public:
    virtual void quack();
}

class Quack : public QuackBehavior
{
public:
    virtual void quack()
    {
        std::cout << "嘎嘎嘎" << std::endl;
    }
}

class MuteQuack : public QuackBehavior
{
public:
    virtual void quack()
    {
        std::cout << "嘎你妹" << std::endl;
    }
}

• 使用上面的算法组合出真正的鸭子和模型鸭子

class LovelyDuck : public Duck
{
    LovelyDuck()
    {
        m_flyBehavior = FlyWithWings();
        m_quackBehavior = Quack();
    }
}

class ModelDuck : public Duck
{
    ModelDuck()
    {
        m_flyBehavior = FlyNoWay();
        m_quackBehavior = MuteQuack();
    }
}

int main()
{
    Duck &lovelyDuck = LovelyDuck();
    Duck &ModelDuck = ModelDuck();

    lovelyDuck.fly();
    lovelyDuck.quack();

    ModelDuck.fly();
    ModelDuck.quack();
    return 0;
}

模式思考:

• 优点: 策略模式组合使用算法族，使软件高复用，灵活
• 缺点: