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:

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Answer 1

First, some ADL helping:

namespace notstd {
  namespace adl_helper {
    using std::to_string;

    template
    std::string as_string( T&& t ) {
      return to_string( std::forward(t) );
    }
  }
  template
  std::string to_string( T&& t ) {
    return adl_helper::as_string(std::forward(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.