C++：当一个元素被添加到set中时，如何调用函数？

#include <iostream>
#include <set>

struct MyElement {
    int value;
    // 其他成员...
};

struct CompareAndCall {
    bool operator()(const MyElement& lhs, const MyElement& rhs) const {
        // 比较逻辑...
        bool result = lhs.value < rhs.value;
        
        // 调用函数
        if (result) {
            std::cout << "Element added: " << lhs.value << std::endl;
        }
        
        return result;
    }
};

int main() {
    std::set<MyElement, CompareAndCall> mySet;
    
    MyElement elem1{10};
    mySet.insert(elem1); // 这里会调用CompareAndCall中的函数
    
    return 0;
}

#include <iostream>
#include <set>

struct MyElement {
    int value;
    // 其他成员...
};

bool onElementAdded(const MyElement& elem) {
    std::cout << "Element added: " << elem.value << std::endl;
    return true;
}

int main() {
    std::set<MyElement> mySet;
    
    MyElement elem1{10};
    auto result = mySet.insert(elem1);
    if (result.second) { // 如果元素被添加
        onElementAdded(*result.first); // 调用函数
    }
    
    return 0;
}

#include <iostream>
#include <set>
#include <vector>

class Observer {
public:
    virtual void onElementAdded(int value) = 0;
};

class MySetObserver : public Observer {
public:
    void onElementAdded(int value) override {
        std::cout << "Element added: " << value << std::endl;
    }
};

class ObservableSet {
    std::set<int> elements;
    std::vector<Observer*> observers;

public:
    void addObserver(Observer* observer) {
        observers.push_back(observer);
    }

    void addElement(int value) {
        elements.insert(value);
        for (Observer* observer : observers) {
            observer->onElementAdded(value);
        }
    }
};

int main() {
    ObservableSet mySet;
    MySetObserver observer;
    
    mySet.addObserver(&observer);
    mySet.addElement(10); // 这里会调用观察者的onElementAdded方法
    
    return 0;
}