Generic implementation of operator<< function in terms of the dump member function

Question

All my classes implement a dump member function, e.g.:

struct A {
    template 
    std::basic_ostream &
         


        

Answer 1

template 
auto operator<< (std::basic_ostream & str, const T & t) -> decltype(t.dump(str))
{
    static_assert(std::is_same
                    &>::value, 
                  ".dump(ostream&) does not return ostream& !");

    return t.dump(str);
}

This overloads operator<< only for types that define an appropriate dump member.

Edit: added static_assert for better messages.