C++ 设计模式 《小明的奶茶加料风波》

👨‍🎓 模式名称：装饰器模式（Decorator Pattern）

👦 小明最近上线了校园奶茶配送功能，业务火爆，大家都在加料：
有的同学要加波霸 🟤，有的要加椰果 🥥，还有的要加奶盖 🥛。
但每个“加料”组合都要写一个新类？小明一开始不以为意，直到……

❌ 没使用装饰器模式的惨状：

#include <iostream>
#include <string>class MilkTea {
public:virtual std::string getDescription() = 0;virtual double cost() = 0;virtual ~MilkTea() {}
};class OriginalMilkTea : public MilkTea {
public:std::string getDescription() override {return "原味奶茶";}double cost() override {return 8.0;}
};class MilkTeaWithBoba : public MilkTea {
public:std::string getDescription() override {return "原味奶茶 + 波霸";}double cost() override {return 10.0;}
};class MilkTeaWithBobaAndCheese : public MilkTea {
public:std::string getDescription() override {return "原味奶茶 + 波霸 + 奶盖";}double cost() override {return 13.0;}
};int main() {MilkTea* tea1 = new OriginalMilkTea();MilkTea* tea2 = new MilkTeaWithBoba();MilkTea* tea3 = new MilkTeaWithBobaAndCheese();std::cout << tea3->getDescription() << " 价格：¥" << tea3->cost() << std::endl;delete tea1;delete tea2;delete tea3;return 0;
}

💥 小明懵了：

加个椰果再写个类？
波霸 + 奶盖 + 椰果再写？
🍵 加料 2^N 种组合，类数直接爆炸！

✅ 使用装饰器模式后：灵活加料，优雅解耦！

#include <iostream>
#include <string>
#include <memory>// 奶茶基类
class MilkTea {
public:virtual std::string getDescription() = 0;virtual double cost() = 0;virtual ~MilkTea() {}
};// 原味奶茶
class OriginalMilkTea : public MilkTea {
public:std::string getDescription() override {return "原味奶茶";}double cost() override {return 8.0;}
};// 装饰器基类
class ToppingDecorator : public MilkTea {
protected:std::shared_ptr<MilkTea> tea;
public:ToppingDecorator(std::shared_ptr<MilkTea> t) : tea(t) {}
};// 加波霸
class Boba : public ToppingDecorator {
public:Boba(std::shared_ptr<MilkTea> t) : ToppingDecorator(t) {}std::string getDescription() override {return tea->getDescription() + " + 波霸🟤";}double cost() override {return tea->cost() + 2.0;}
};// 加奶盖
class Cheese : public ToppingDecorator {
public:Cheese(std::shared_ptr<MilkTea> t) : ToppingDecorator(t) {}std::string getDescription() override {return tea->getDescription() + " + 奶盖🥛";}double cost() override {return tea->cost() + 3.0;}
};// 加椰果
class Coconut : public ToppingDecorator {
public:Coconut(std::shared_ptr<MilkTea> t) : ToppingDecorator(t) {}std::string getDescription() override {return tea->getDescription() + " + 椰果🥥";}double cost() override {return tea->cost() + 1.5;}
};int main() {// 原味奶茶 + 波霸 + 奶盖 + 椰果！std::shared_ptr<MilkTea> order = std::make_shared<OriginalMilkTea>();order = std::make_shared<Boba>(order);order = std::make_shared<Cheese>(order);order = std::make_shared<Coconut>(order);std::cout << "🎉 " << order->getDescription() << " 价格：¥" << order->cost() << std::endl;return 0;
}

🧠 总结：装饰器模式的价值

✅ 适用场景

• 不同功能组合需要动态叠加（如小明的加料奶茶🍵、网页组件、技能系统等）

• 不想通过继承创建过多子类

• 需要在运行时添加功能而非编译期