装饰者模式

装饰者模式：动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

基本模型：

利用基本组件和装饰物共同继承自一个超类的设计，在超类中拥有所需的方法接口，在所有的装饰物类中保存超类的指针，将此指针视为此装饰物装饰之前的状态，基于此实现此装饰物装饰后的状态，所有的装饰物都有之前和之后的状态，也即只完成属于自己的那个步骤，因此符合开放关闭原则。核心就是利用多态来保存各个步骤的属性，而形式完全一致。

一个例子：

#include<iostream>
#include<string>
using namespace std;
class Beverage
{
public:
	virtual void getDescription() = 0;
	virtual float cost() = 0;
};

class HouseBlend :public Beverage
{
public :
	void getDescription()override{ cout << "HouseBlend ----- $" << cost()<<endl; }
	float cost()override{ return 2.1; }
};

class DarkRoast :public Beverage
{
public:
	void getDescription()override{ cout << "DarkRoast ----- $" << cost() << endl; }
	float cost()override{ return 3.0f; }
};

class Espresso :public Beverage
{
public:
	void getDescription()override{ cout << "Espresso ----- $" << cost() << endl; }
	float cost()override{ return 2.3f; }
};

class Decaf :public Beverage
{
public:
	void getDescription() override{ cout << "Decaf ----- $" << cost() << endl; }
	float cost() override{ return 3.1f; }
};

class CondimentDecorator :public Beverage
{
public:
	Beverage *_beverage;
};

class Milk :public CondimentDecorator
{
public:
	Milk(Beverage *beverage){ _beverage = beverage; };
	void getDescription() override { _beverage->getDescription(); cout << "Milk ----- $0.8" << endl; }
	float cost() override{ return 0.8f+_beverage->cost(); }
};

class Mocha :public CondimentDecorator
{
public:
	Mocha(Beverage *beverage){ _beverage = beverage; }
	void getDescription() override { _beverage->getDescription(); cout << "Mocha ----- $0.6" << endl; }
	float cost() override { return 0.6f + _beverage->cost(); }
};

class Soy :public CondimentDecorator
{
public:
	Soy(Beverage *beverage){ _beverage = beverage; }
	void getDescription() override { _beverage->getDescription(); cout << "Soy ----- $0.4" << endl; }
	float cost() override { return 0.4f + _beverage->cost(); }
};

class Whip :public CondimentDecorator
{
public:
	Whip(Beverage *beverage){ _beverage = beverage; }
	void getDescription() override { _beverage->getDescription(); cout << "Whip ----- $0.3" << endl; }
	float cost() override{ return 0.3f + _beverage->cost(); }
};

int main()
{
	Beverage *beverage =new DarkRoast();
	beverage =new Milk(beverage);
	beverage = new Mocha(beverage);
	beverage = new Whip(beverage);
	beverage->getDescription();
	cout<<"Total : $"<<beverage->cost()<<endl;

	Beverage *beverage1 = new Decaf();
	beverage1 = new Soy(beverage1);
	beverage1 = new Mocha(beverage1);
	beverage1 = new Mocha(beverage1);
	beverage1 = new Milk(beverage1);
	beverage1->getDescription();
	cout << "Total : $"<<beverage1->cost() << endl; 
	system("pause");
	return 0;
}

结果：