std::experimental::ranges::difference_type(3)

NAME
std::experimental::ranges::difference_type - std::experimental::ranges::difference_type

Synopsis
   Defined in header <experimental/ranges/iterator>
   template< class I > (1)
   struct difference_type { };
   template< class T > (2)
   struct difference_type<T*>;
   template< class T > (3)
   struct difference_type<const T> : difference_type<std::decay_t<T>> { };
   template <class T>
   requires requires { typename T::difference_type; } (4)
   struct difference_type<T>;
   template <class T>
   requires !requires { typename T::difference_type; } && (5)
   requires(const T& a, const T& b) { { a - b } -> Integral; }
   struct difference_type<T>;
   Computes the associated difference type of the type I, if any. Users may specialize
   difference_type for a program-defined type.
   1) Primary template is an empty struct.
   2) Specialization for pointers. If T is an object type, provides a member type type
   equal to std::ptrdiff_t. Otherwise, there is no member type.
   3) Specialization for const-qualified types.
   4) Specialization for types that define a public and accessible member type
   difference_type. Provides a member type type equal to T::difference_type.
   5) Specialization for types that do not define a public and accessible member type
   difference_type but do support subtraction. Provides a member type type equal to
   std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>.
  Helper alias template
   template< class T > (ranges TS)
   using difference_type_t = typename ranges::difference_type<T>::type;

Example
    This section is incomplete
    Reason: no example

See also
                       specifies that a Semiregular type can be incremented with pre-
   WeaklyIncrementable and post-increment operators
                       (concept)
                       compatibility traits class that collects an iterator’s
   iterator_traits associated types
                       (alias template)