C++框架最佳实践中的设计模式

// 目标接口
class ITarget {
public:
    virtual void request() = 0;
};

// 适配器类，将 Adaptee 适配为 ITarget
class Adapter : public ITarget {
    Adaptee* adaptee_;
public:
    Adapter(Adaptee* adaptee) : adaptee_(adaptee) {}
    virtual void request() override {
        adaptee_->specificRequest();
    }
};

// 具体类
class Adaptee {
public:
    virtual void specificRequest() {
        // 具体实现
    }
};

int main() {
    Adaptee* adaptee = new Adaptee();
    ITarget* target = new Adapter(adaptee);
    target->request();
    return 0;
}

// 单例类
class Singleton {
private:
    static Singleton* instance_;
    Singleton() {}
public:
    static Singleton* getInstance() {
        if (instance_ == nullptr) {
            instance_ = new Singleton();
        }
        return instance_;
    }
};

int main() {
    Singleton* instance1 = Singleton::getInstance();
    Singleton* instance2 = Singleton::getInstance();
    assert(instance1 == instance2); // 始终返回同一个实例
    return 0;
}

// 目标类
class Subject {
public:
    virtual void attach(Observer* observer) = 0;
    virtual void detach(Observer* observer) = 0;
    virtual void notify() = 0;
};

// 观察者类
class Observer {
public:
    virtual void update() = 0;
};

class ConcreteSubject : public Subject {
    std::vector<Observer*> observers_;
    int state_;
public:
    void attach(Observer* observer) override {
        observers_.push_back(observer);
    }
    void detach(Observer* observer) override {
        auto it = std::find(observers_.begin(), observers_.end(), observer);
        if (it != observers_.end()) {
            observers_.erase(it);
        }
    }
    void notify() override {
        for (auto observer : observers_) {
            observer->update();
        }
    }
    int getState() const { return state_; }
    void setState(int state) {
        state_ = state;
        notify();
    }
};

class ConcreteObserver : public Observer {
    ConcreteSubject* subject_;
public:
    ConcreteObserver(ConcreteSubject* subject) : subject_(subject) {}
    void update() override {
        int state = subject_->getState();
        // 根据状态更新自身状态
    }
};

int main() {
    ConcreteSubject* subject = new ConcreteSubject();
    ConcreteObserver* observer1 = new ConcreteObserver(subject);
    ConcreteObserver* observer2 = new ConcreteObserver(subject);
    subject->attach(observer1);
    subject->attach(observer2);

    subject->setState(10);
    subject->setState(20);
    return 0;
}