The key point is: a decorator is-a component and has-a component.
#include <iostream>
class Component {
public:
virtual void Operation() = 0;
};
class ConcreteComponent : public Component {
public:
void Operation() override {
std::cout << "Concrete component operation\n";
}
};
class Decorator : public Component {
protected:
Component* component;
public:
Decorator(Component* c) : component(c) {}
void Operation() override {
std::cout << "Decorator\n";
component->Operation(); // 呼叫被裝飾對象的操作
}
};
class ConcreteDecoratorA : public Decorator {
public:
ConcreteDecoratorA(Component* c) : Decorator(c) {}
void Operation() override {
component->Operation();
// 新增額外責任
std::cout << "Decorator A operation." << std::endl;
}
};
class ConcreteDecoratorB : public Decorator {
public:
ConcreteDecoratorB(Component* c) : Decorator(c) {}
void Operation() override {
component->Operation();
// 新增額外責任
std::cout << "Decorator B operation." << std::endl;
}
};
int main() {
Component* core = new ConcreteComponent();
Component* decorator1 = new ConcreteDecoratorA(core);
Component* decorator2 = new ConcreteDecoratorB(decorator1);
decorator2->Operation();
}
/*
Executor x86-64 gcc 13.2 (C++, Editor #1)
-std=c++20
Program returned: 0
Program stdout
Concrete component operation
Decorator A operation.
Decorator B operation.
*/分析：
With C++11, using unique_ptr:
#include <iostream>
#include <memory>
class Component {
public:
virtual void Operation() = 0;
};
class ConcreteComponent : public Component {
public:
void Operation() override {
std::cout << "Concrete component operation\n";
}
};
class Decorator : public Component {
protected:
std::unique_ptr<Component> component;
public:
Decorator(std::unique_ptr<Component> c) : component(std::move(c)) {}
void Operation() override {
component->Operation();
}
};
class ConcreteDecoratorA : public Decorator {
public:
ConcreteDecoratorA(std::unique_ptr<Component> c) : Decorator(std::move(c)) {}
void Operation() override {
component->Operation();
std::cout << "Decorator A operation." << std::endl;
}
};
class ConcreteDecoratorB : public Decorator {
public:
ConcreteDecoratorB(std::unique_ptr<Component> c) : Decorator(std::move(c)) {}
void Operation() override {
component->Operation();
std::cout << "Decorator B operation." << std::endl;
}
};
int main() {
std::unique_ptr<Component> core = std::make_unique<ConcreteComponent>();
std::unique_ptr<Component> decorator1 = std::make_unique<ConcreteDecoratorA>(std::move(core));
std::unique_ptr<Component> decorator2 = std::make_unique<ConcreteDecoratorB>(std::move(decorator1));
decorator2->Operation();
}