to_string & println with variadic templates

println

template< class S> void print_with(S& s, char delim) {}
template< class S, typename T> void print_with(S& s, char delim, const T& t) { s<<t; }
template <class S, typename T, typename... Args> void print_with(S& s, char delim, const T& t, const Args& ...args) { s << t; if (delim) s << delim; print_with(s, delim, args...); }

template <typename... Args>
std::string to_string_with(char delim, const Args& ...args) { std::stringstream ss; print_with(ss, delim, args...); return ss.str(); }

template <typename... Args> std::string to_string(const Args& ...args) { return to_string_with('\x00', args...); }
template <typename... Args> std::ostream& print(std::ostream& out, const Args& ...args)   { print_with(out, '\x00', args...); return out;}
template <typename... Args> std::ostream& println(std::ostream& out, const Args& ...args) { print_with(out, '\x00', args...); out << std::endl; return out;}