C++实现设计模式之装饰者模式详解

//抽象组件类-饮料
class Beverage
{
public:
	Beverage() :m_description("Unknown Beverage")
	{
	}
	virtual std::string getDescription(){ return m_description; }
	virtual double cost() = 0;
protected:
	std::string m_description;
};
//抽象装饰者类-调料，继承自饮料类
class CondimentDecorator :public Beverage
{
public:
	CondimentDecorator(Beverage* berverge) 
		:m_beverage(berverge)
	{
	}
	virtual std::string getDescription() = 0;//定义成纯虚函数，是为了强制子类实例化时必须实现它。
protected:
	Beverage* m_beverage;
};

//三个具体组件
class DarkRoast :public Beverage
{
public:
	DarkRoast()
	{
		m_description = "DarkRoast";
	}
	double cost()
	{
		return 2.99;
	}
};
class Espresso :public Beverage
{
public:
	Espresso()
	{
		m_description = "Espresso";
	}
	double cost()
	{
		return 1.99;
	}
};
class HouseBlend :public Beverage
{
public:
	HouseBlend()
	{
		m_description = "HouseBlend";
	}
	double cost()
	{
		return 0.89;
	}
};

//两个具体装饰者
class Mocha :public CondimentDecorator
{
public:
	Mocha(Beverage* beverage) :CondimentDecorator(beverage)
	{
	}
	std::string getDescription()
	{
		return  m_beverage->getDescription() + " Mocha";
	}
	double cost()
	{
		return 0.2 + m_beverage->cost();
	}
};
class Milk :public CondimentDecorator
{
public:
	Milk(Beverage* beverage) :CondimentDecorator(beverage)
	{
	}
	std::string getDescription()
	{
		return  m_beverage->getDescription() + " Milk";
	}
	double cost()
	{
		return 0.5 + m_beverage->cost();
	}
};

//测试代码
int main()
{
	//不加调料的Espresso
	Beverage* beverage = new Espresso();
	std::cout << beverage->getDescription() << " ￥" << beverage->cost() << std::endl;
	//加双倍摩卡和奶泡的DarkRoast
	Beverage* beverage2 = new DarkRoast();
	beverage2 = new Mocha(beverage2);
	beverage2 = new Mocha(beverage2);
	beverage2 = new Milk(beverage2);
	std::cout << beverage2->getDescription() << " ￥" << beverage2->cost() << std::endl;
	//加双倍奶泡的和一份摩卡的HouseBlend
	Beverage* beverage3 = new HouseBlend();
	beverage3 = new Mocha(beverage3);
	beverage3 = new Milk(beverage3);
	beverage3 = new Milk(beverage3);
	std::cout << beverage3->getDescription() << " ￥" << beverage3->cost() << std::endl;
	system("pause");
	delete beverage;
	delete beverage2;
	delete beverage3;
}