The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
template<typename List>
struct IsEmpty {
static constexpr bool value = false;
};
template<>
struct IsEmpty<Nil> {
static constexpr bool value = true;
};