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
#include <iterator>
#include "enableif.hpp"
#include "isconvertible.hpp"
template<typename Iterator>
constexpr bool IsInputIterator =
IsConvertible<
typename std::iterator_traits<Iterator>::iterator_category,
std::input_iterator_tag>;
template<typename T>
class Container {
public:
// construct from an input iterator sequence:
template<typename Iterator,
typename = EnableIf<IsInputIterator<Iterator>>>
Container(Iterator first, Iterator last);
// convert to a container so long as the value types are convertible:
template<typename U, typename = EnableIf<IsConvertible<T, U>>>
operator Container<U>() const;
};