How to cast to default string?

Question

C++ / C#

#include <iostream>
#include <string>

class A {
private:
    std::string s = std::string("hello");
public:
    operator std::string& () {return s;}
    //operator const char* () {return s.c_str();}
};

int main() {
    A a;
    std::cout << a << '\n';
}

If you do not leave operator const char*, then "no known conversion for argument", although the conversion to std::string& is defined. Maybe the output operator for std::string is not defined? Changing the type to an unreferenced type or to a constant reference does not help. Though at operator const char* works.

Answer 1

So it's implicitly impossible.

Answer 2

Need to explicitly convert for the cout operator

#include <iostream>
#include <string>

class A {
private:
    std::string s = std::string("hello");
public:
    operator std::string& () {return s;}
    //operator const char* () {return s.c_str();}
};

int main() {
    A a;
    std::cout << (std::string)a << '\n';
}