设计模式笔记：装饰器模式

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是一种结构型设计模式，允许用户在不改变现有对象结构的情况下向现有对象添加新的功能。

示例

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#include <iostream>
using namespace std;

class Car {
public:
    virtual void ShowMessage()
    {
        cout << "Base Car" << endl;
    }
};

class Decorator : public Car{
public:
    Decorator() = default;
    Decorator(Car *car) : car_(car) {}
    void ShowMessage()
    {
        if (car_) {
            car_->ShowMessage();
            cout << "Add function!" << endl;
        }
    }

private:
    Car* car_ = nullptr;
};

class DecoratorA : public Decorator{
public:
    DecoratorA(Car *car) : car_(car) {}
    void ShowMessage()
    {
        if (car_) {
            car_->ShowMessage();
            cout << "Add auto {ai} function!" << endl;
        }
    }

private:
    Car* car_ = nullptr;
};

class DecoratorB : public Decorator{
public:
    DecoratorB(Car *car) : car_(car) {}
    void ShowMessage()
    {
        if (car_) {
            car_->ShowMessage();
            cout << "Add auto {run} function!" << endl;
        }
    }

private:
    Car* car_ = nullptr;
};

int main()
{
    Car* car = new Car();
    car->ShowMessage();
    cout << "---------" << endl;
    Car* addA = new DecoratorA(car);
    addA->ShowMessage();
    cout << "=========" << endl;
    Car* addB = new DecoratorB(addA);
    addB->ShowMessage();
    return 0;
}
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Base Car
---------
Base Car
Add auto {ai} function!
=========
Base Car
Add auto {ai} function!
Add auto {run} function!

总结：核心在于装饰器基类继承原始基类，使得能够动态增加功能