装饰者模式

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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：

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