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, typename T, unsigned N = 0,
bool Empty = IsEmpty<List>::value>
struct FindIndexOfT;
// recursive case:
template<typename List, typename T, unsigned N>
struct FindIndexOfT<List, T, N, false>
: public IfThenElse<std::is_same<Front<List>, T>::value,
std::integral_constant<unsigned, N>,
FindIndexOfT<PopFront<List>, T, N+1>>
{
};
// basis case:
template<typename List, typename T, unsigned N>
struct FindIndexOfT<List, T, N, true>
{
};