C++实现装饰模式，为什么中间环节被“跳过”了？

Question

#include<iostream>
using namespace std;

class Component
{
public:
    virtual void operation() 
    {
        cout << "Component\n";
    }
};

class Decorator: public Component
{
protected:
    Component component;
public:
    void setComponent(Component component)
    {
        this->component = component;
    }
    virtual void operation()
    {
        component.operation();
    }
};

class ConcreteDecoratorA: public Decorator
{
public:
    virtual void operation()
    {
        Decorator::operation();
        cout << "ConcreteDecoratorA\n";
    }
};

class ConcreteDecoratorB : public Decorator
{
public:
    virtual void operation()
    {
        Decorator::operation();
        cout << "ConcreteDecoratorB\n";
    }
};

int main()
{
    Component c;
    ConcreteDecoratorA a;
    ConcreteDecoratorB b;
    a.setComponent(c);
    b.setComponent(a);
    b.operation();
    return 0;
}

输出：
Component
ConcreteDecoratorB

为什么不会输出“ConcreteDecoratorA”呢？

Answer 1

b.setComponent(a);的时候的方法是类Decorator里的
参数是Component，而a的类型是ConcreteDecoratorA，被退化为Decorator，再退化为Component
所以自始至终都没有使用过ConcreteDecoratorA:类里的任何东西，自然不会输出ConcreteDecoratorA