Making a user-defined class std::to_string-able

Question

I know it seems too much Java or C#. However, is it possible/good/wise to make my own class valid as an input for the function std::to_string ? Example:

class my_class{
public:
std::string give_me_a_string_of_you() const{
    return "I am " + std::to_string(i);
}
int i;
};

void main(){
    my_class my_object;
    std::cout<< std::to_string(my_object);
}

If there is no such thing (and I think that), what is the best way to do it?

Answer 1

First, some ADL helping:

namespace notstd {
  namespace adl_helper {
    template<class T>
    std::string as_string( T&& t ) {
      using std::to_string;
      return to_string( std::forward<T>(t) );
    }
  }
  template<class T>
  std::string to_string( T&& t ) {
    return adl_helper::as_string(std::forward<T>(t));
  }
}

notstd::to_string(blah) will do an ADL-lookup of to_string(blah) with std::to_string in scope.

We then modify your class:

class my_class{
public:
  friend std::string to_string(my_class const& self) {
    return "I am " + notstd::to_string(self.i);
  }
  int i;
};

and now notstd::to_string(my_object) finds the proper to_string, as does notstd::to_string(7).

With a touch more work, we can even support .tostring() methods on types to be auto-detected and used.

Live example