C++如何实现一个观察者设计模式？（代码示例）

class Observer {
public:
    virtual ~Observer() = default;
    virtual void update(const std::string& message) = 0;
};

#include 
#include 
#include 

class Subject {
protected:
    std::vector> observers;

public:
    void attach(std::shared_ptr obs) {
        if (obs) observers.push_back(obs);
    }

    void detach(std::shared_ptr obs) {
        observers.erase(
            std::remove(observers.begin(), observers.end(), obs),
            observers.end()
        );
    }

    void notify(const std::string& message) {
        for (const auto& obs : observers) {
            if (obs) obs->update(message);
        }
    }
};

class TemperatureSensor : public Subject {
private:
    double temperature = 0.0;

public:
    void setTemperature(double temp) {
        temperature = temp;
        notify("Temperature changed to " + std::to_string(temp) + "°C");
    }
};

class Logger : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "[LOG] " << message << std::endl;
    }
};

class Display : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "[DISPLAY] " << message << std::endl;
    }
};

int main() {
    TemperatureSensor sensor;
    auto logger = std::make_shared();
    auto display = std::make_shared();

    sensor.attach(logger);
    sensor.attach(display);

    sensor.setTemperature(25.5); // 输出两条消息
    sensor.detach(logger);
    sensor.setTemperature(26.0); // 只有 display 响应

    return 0;
}