設計模式：策略模式（1）C++版

策略模式：定義了算法族，將其封裝起來，在其內部可相互替換。讓它的變化獨立於需要它的客戶類。

其C++例子實現如下：

/*
* CONTENTS: DESIGN PATTERN, STRATEGY PATTERN
*   AUTHOR: YAO H. WANG
*     TIME: 2013-10-17 17:08:34
*  EDITION: 1
*
* ALL RIGHTS RESERVED!
*/

#include <iostream>

using namespace std;

/*
* 原則1：把變化的部分和不變的部分分開。
* 飛行行爲和呱呱叫行爲
*/

//飛行行爲
class FlyBehavior
{
public:
	virtual void fly() = 0;
};

class FlyWithWings: public FlyBehavior
{
public:
	void fly()
	{
		cout << "I'm flying!!" << endl;
	}
};

class FlyNoWay: public FlyBehavior
{
public:
	void fly()
	{
		cout << "I can't fly" << endl;
	}
};

class FlyRocketPowered: public FlyBehavior
{
public:
	void fly()
	{
		cout <<  "I'm flying with a rocket!" << endl;
	}
};

//呱呱叫行爲
class QuackBehavior
{
public:
	virtual void quack() = 0;
};

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

class MuteQuack: public QuackBehavior
{
public:
	void quack()
	{
		cout << "<< Silence >>" << endl;
	}
};

class Squeak: public QuackBehavior
{
public:
	void quack()
	{
		cout << "Squeak" << endl;
	}
};

//客戶類——鴨子
class Duck
{
public:
	/*
	* 原則2：多組合，少繼承
	*/
	FlyBehavior *flyBehavior;
	QuackBehavior *quackBehavior;

private:
	virtual void display() = 0;

public:
	virtual void performFly()
	{
		flyBehavior->fly();
	}
	virtual void performQuack()
	{
		quackBehavior->quack();
	}
	virtual void setFlyBehavior(FlyBehavior *fb)
	{
		flyBehavior = fb;
	}
	virtual void setQuackBehavior(QuackBehavior *qb)
	{
		quackBehavior = qb;
	}

	virtual ~Duck()
	{
	}
};

class MallardDuck: public Duck
{
public:
	MallardDuck()
	{
		flyBehavior = new FlyWithWings();
		quackBehavior = new Quack();
	}

	void display()
	{
		cout << "I'm a real Mallard duck" << endl;
	}

	~MallardDuck()
	{
		delete flyBehavior;
		delete quackBehavior;
	}
};

class ModelDuck: public Duck
{
public:
	ModelDuck()
	{
		flyBehavior = new FlyNoWay();
		quackBehavior = new Quack();
	}

	void display()
	{
		cout << "I'm a model duck" << endl;
	}

	~ModelDuck()
	{
		delete flyBehavior;
		delete quackBehavior;
	}
};

//測試
void main()
{
	/*
	* 原則3： 針對接口編程，而不是針對實現編程
	*/
	Duck* mallard = new MallardDuck();
	mallard->performFly();
	mallard->performQuack();

	Duck* model = new ModelDuck();
	model->performFly();
	model->setFlyBehavior(new FlyRocketPowered());
	model->performFly();

	delete mallard;
	delete model;
}