装饰器设计模式就是在原有类的基础上增加一些装饰功能,顶层的接口实现子类作为要实例化的对象,传到装饰器中,增加特定装饰器的功能,我习惯用代码解释,直接看代码.

这段代码包含了两个例子,都是先定义一个顶层的接口,然后定义装饰器抽象类,里面维护了一个接口的指针,在具体的装饰器中,通过构造函数传递顶层接口的实现子类指针,借助多态机制实现装饰功能.

#include <bits/stdc++.h>

using namespace std;

/**----------------------------------------------------**/
class Cake {
public:
    virtual void showCake() = 0;
    virtual ~Cake(){};
    std::string name;
};

class ConcreteCake : public Cake {
public:
    ConcreteCake()
    {
        name = "原始蛋糕";
    }
    void showCake() { std::cout << name.c_str() << std::endl; };
    virtual ~ConcreteCake(){};
};

class CakeDecrator : public Cake {
protected:
    Cake* pCake; //维护一个Cake对象的引用,为Cake对象添加装饰
public:
    virtual void showCake() = 0;
    virtual ~CakeDecrator(){};
};

class CakeDecratorCholate : public CakeDecrator {
public:
    CakeDecratorCholate(Cake* pCake)
    {
        this->pCake = pCake;
    }
    void showCake()
    {
        this->name = pCake->name + "加巧克力";
        std::cout << name.c_str() << std::endl;
    }
    virtual ~CakeDecratorCholate(){};
};
/**-----------------------------------------------------------------------**/

class Shape {
public:
    virtual void draw() = 0;
    virtual ~Shape(){}
    string name;
};

class Circle : public Shape {
public:
    Circle()
    {
        this->name = "circle";
    }
    void draw() override
    {
        cout << this->name << endl;
    }
    virtual ~Circle()
    {
    }
};

class Decorator : public Shape {
public:
    virtual void draw() = 0;
    virtual ~Decorator()
    {
    }
    Shape* shape;
};

class RedDecorator : public Decorator {
public:
    RedDecorator(Shape* s)
    {
        //this->name = s->name + " red";
        shape = s;
    }
    void draw()
    {
        this->name = shape->name + " red";
        cout << this->name << endl;
    }
    virtual ~RedDecorator() {}
};

int main()
{
    // Circle* circle = new Circle;
    // circle->draw();
    //RedDecorator* redCircle = new RedDecorator(circle);
    //redCircle->draw();
    ConcreteCake* cake = new ConcreteCake();
    CakeDecratorCholate* cholateCake = new CakeDecratorCholate(cake);
    cholateCake->showCake();

    shared_ptr<Shape> circle(new Circle);
    //Shape* circle = new Circle;
    RedDecorator* redCircle = new RedDecorator(circle.get());
    redCircle->draw();
}