#include <type_traits>
template<typename Type>
auto operator<<(
	std::ostream& out, const Type& person)
	-> std::enable_if_t<std::is_same<Person, Type>::value, std::ostream&>
{
	return out << "first_name=" << person.get_first_name()
		<< ",last_name=" << person.get_last_name();
}