介紹
裝飾者模式在物件上動態加入其他行為或職責，提供除了創建子類外的另一種方法。

以下範例是利用裝飾者模式，在義大利pizza上加入大量的鳳梨。

C++範例

#include <iostream>

class Pizza
{
public:
    virtual ~Pizza() {}
    virtual void Make() = 0;

protected:
    Pizza() {}
};

class ItalyPizza : public Pizza
{
public:
    ItalyPizza() {}
    ~ItalyPizza() {}

    void Make() override
    {
        std::cout << "Pizza made with italy formula" << std::endl;
    }
};

class Decorator : public Pizza
{
public:
    Decorator(Pizza *pizza)
    {
        m_Pizza = pizza;
    }

    virtual ~Decorator()
    {
        if (m_Pizza)
            delete m_Pizza;
    }

    virtual void PutSomethingOnPizza() = 0;

protected:
    Pizza *m_Pizza;
};

class EvilDecorator : public Decorator
{
public:
    EvilDecorator(Pizza *pizza) : Decorator(pizza)
    {
    }

    void Make() override
    {
        m_Pizza->Make();
        PutSomethingOnPizza();
    }

    void PutSomethingOnPizza() override
    {
        std::cout << "Put tons of pineapple on pizza" << std::endl;
    }
};

int main()
{
    Pizza *italyPizza = new ItalyPizza();
    Decorator *dec = new EvilDecorator(italyPizza);
    dec->Make();

    delete dec;
    return 0;
}

Output:

Pizza made with italy formula
Put tons of pineapple on pizza