How to convert anything to string implicitly?

Question

My goal is to design a String class that decorates std::string in order to provide some functionality my program needs. One functionality I want to add is the ability to con

Answer 1

Instead of declaring the output operator in the surrounding namespace, only declare it as a friend of the String class:

class String {
public:
    // This must be implemented inline here
    friend std::ostream& operator<<(std::ostream& o, const String& s) {
        return o << _str; // for example
    }

    template
    String(t_value value) {
       std::ostringstream oss;
       oss << value;
      _str = oss.str();
    }
private:
    std::string _str;
};

Now it can only be found by argument-dependent lookup, and so will only be considered if the second argument really is of type String, not just convertible to it. Therefore, it won't be considered as a candidate for os << value in the constructor, giving a compile error rather than a run-time death spiral if there is no other candidate.