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，装饰着提供了比继承更有弹性的替代方案。

#include <iostream>
#include <string>

using namespace std;


struct Beverage {
public:
    virtual string getDescription() {
        return description;
    }

    virtual double cost() = 0;

protected:
    string description;
};


struct HouseBlend : public Beverage {
public:
    HouseBlend() {
        description = "HouseBlend";
    }

    virtual double cost() {
        return 2.0;
    }
};

struct DarkRoast : public Beverage {
public:
    DarkRoast() {
        description = "DarkRoast";
    }

    virtual double cost() {
        return 2.1;
    }
};

struct Espresso : public Beverage {
public:
    Espresso() {
        description = "Espresso";
    }

    virtual double cost() {
        return 2.2;
    }
};

struct Decaf : public Beverage {
public:
    Decaf() {
        description = "Decaf";
    }

    virtual double cost() {
        return 2.3;
    }
};


struct CondimentDecorator : public Beverage {
public:
    virtual string getDescription() = 0;
};

struct Milk : public CondimentDecorator {
public:
    Milk(Beverage *mbeverage) {
        beverage = mbeverage;
    }

    virtual double cost() {
        return 0.1 + beverage->cost();
    }

    virtual string getDescription() {
        return beverage->getDescription() + ", Milk";
    }

private:
    Beverage *beverage;
};

struct Mocha : public CondimentDecorator {
public:
    Mocha(Beverage *mbeverage) {
        beverage = mbeverage;
    }

    virtual double cost() {
        return 0.2 + beverage->cost();
    }

    virtual string getDescription() {
        return beverage->getDescription() + ", Mocha";
    }
private:
    Beverage *beverage;
};

struct Soy : public CondimentDecorator {
public:
    Soy(Beverage *mbeverage) {
        beverage = mbeverage;
    }

    virtual double cost() {
        return 0.3 + beverage->cost();
    }

    virtual string getDescription() {
        return beverage->getDescription() + ", Soy";
    }
private:
    Beverage *beverage;
};

struct Whip : public CondimentDecorator {
public:
    Whip(Beverage *mbeverage) {
        beverage = mbeverage;
    }

    virtual double cost() {
        return 0.4 + beverage->cost();
    }

    virtual string getDescription() {
        return beverage->getDescription() + ", Whip";
    }
private:
    Beverage *beverage;
};


main()
{
    Beverage *beverage = new HouseBlend();

    beverage = new Milk(beverage);
    beverage = new Whip(beverage);
    beverage = new Soy(beverage);

    cout << beverage->getDescription() << endl;
    cout << beverage->cost() << endl;

}