hasderef.hpp

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 <utility>        // for declval()
#include <type_traits>    // for true_type and false_type

template<typename T>
class HasDereference {
 private:
  template<typename U> struct Identity;
  template<typename U> static std::true_type 
    test(Identity<decltype(*std::declval<U>())>*);
  template<typename U> static std::false_type
    test(...);
 public:
  static constexpr bool value = decltype(test<T>(nullptr))::value;
};