Add iterator_*_t helpers for iterator traits.

- iterator_value_t
- iterator_pointer_t
- iterator_reference_t
- iterator_difference_t
- iterator_system_t

thrust/iterator/detail/iterator_traits.inl

@@ -33,27 +33,36 @@ template<typename Iterator>
   typedef typename thrust::iterator_traits<Iterator>::value_type type;
 }; // end iterator_value
 
+template <typename Iterator>
+using iterator_value_t = typename iterator_value<Iterator>::type;
 
 template<typename Iterator>
   struct iterator_pointer
 {
   typedef typename thrust::iterator_traits<Iterator>::pointer type;
 }; // end iterator_pointer
 
+template <typename Iterator>
+using iterator_pointer_t = typename iterator_pointer<Iterator>::type;
 
 template<typename Iterator>
   struct iterator_reference
 {
   typedef typename iterator_traits<Iterator>::reference type;
 }; // end iterator_reference
 
+template <typename Iterator>
+using iterator_reference_t = typename iterator_reference<Iterator>::type;
 
 template<typename Iterator>
   struct iterator_difference
 {
   typedef typename thrust::iterator_traits<Iterator>::difference_type type;
 }; // end iterator_difference
 
+template <typename Iterator>
+using iterator_difference_t = typename iterator_difference<Iterator>::type;
+
 namespace detail
 {
 
@@ -90,6 +99,8 @@ template<>
   typedef thrust::iterator_system<const int*>::type type;
 }; // end iterator_system<void*>
 
+template <typename Iterator>
+using iterator_system_t = typename iterator_system<Iterator>::type;
 
 template <typename Iterator>
   struct iterator_traversal