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,
template<typename X, typename Y> class F,
typename I,
bool = IsEmpty<List>::value>
class AccumulateT;
// recursive case:
template<typename List,
template<typename X, typename Y> class F,
typename I>
class AccumulateT<List, F, I, false>
: public AccumulateT<PopFront<List>, F,
typename F<I, Front<List>>::Type>
{
};
// basis case:
template<typename List,
template<typename X, typename Y> class F,
typename I>
class AccumulateT<List, F, I, true>
{
public:
using Type = I;
};
template<typename List,
template<typename X, typename Y> class F,
typename I>
using Accumulate = typename AccumulateT<List, F, I>::Type;