std :: map键类必须满足哪些要求才能成为有效键？

#include<iostream>
#include <map>

class MyClass {
public:
    MyClass(int id) : m_id(id) {}

    bool operator<(const MyClass& other) const {
        return m_id< other.m_id;
    }

    MyClass(const MyClass& other) {
        m_id = other.m_id;
    }

    MyClass& operator=(const MyClass& other) {
        m_id = other.m_id;
        return *this;
    }

private:
    int m_id;
};

int main() {
    std::map<MyClass, std::string> my_map;
    MyClass key1(1);
    MyClass key2(2);
    my_map[key1] = "Hello";
    my_map[key2] = "World";

    for (const auto& pair : my_map) {
        std::cout<< pair.first.m_id << ": "<< pair.second<< std::endl;
    }

    return 0;
}