std::ranges::views::adjacent,std::ranges::adjacent_view,std::ranges::views::pairwise(3)

NAME
std::ranges::views::adjacent,std::ranges::adjacent_view,std::ranges::views::pairwise - std::ranges::views::adjacent,std::ranges::adjacent_view,std::ranges::views::pairwise

Synopsis
   Defined in header <ranges>
   template< ranges::forward_range V, std::size_t N >
       requires ranges::view<V> && (N > 0) (1) (since C++23)
   class adjacent_view
       : public ranges::view_interface<adjacent_view<V, N>>
   namespace views {
   template< std::size_t N >
       inline constexpr /* unspecified */ adjacent = /* unspecified (2) (since C++23)
   */ ;
   }
   namespace views {
       inline constexpr auto pairwise = adjacent<2>; (3) (since C++23)
   }
   Call signature
   template< ranges::viewable_range R >
       requires /* see below */ (since C++23)
   constexpr ranges::view auto adjacent<N>( R&& r );
   1) adjacent_view is a range adaptor that takes a view, and produces a view whose
   i^th element (a "window") is a std::tuple that holds N references to the elements of
   the original view, from i^th up to i + N - 1^th inclusively.
   Let S be the size of the original view. Then the size of produced view is:
     * S - N + 1, if S >= N,
     * 0 otherwise, and the resulting view is empty.
   2) The name views::adjacent<N> denotes a RangeAdaptorObject. Given a subexpression e
   and a constant expression N, the expression views::adjacent<N>(e) is
   expression-equivalent to
     * ((void)e, auto(views::empty<tuple<>>)) if N is equal to 0,
     * adjacent_view<views::all_t<decltype((e))>, N>(e) otherwise.
   3) The name views::pairwise denotes a RangeAdaptorObject that behaves exactly as
   views::adjacent<2>.
   adjacent_view always models forward_range, and models bidirectional_range,
   random_access_range, or sized_range if adapted view type models the corresponding
   concept.

Member functions
   constructor constructs a adjacent_view
   (C++23) (public member function)
   begin returns an iterator to the beginning
   (C++23) (public member function)
   end returns an iterator or a sentinel to the end
   (C++23) (public member function)
   size returns the number of elements. Provided only if the underlying
   (C++23) (adapted) range satisfies sized_range.
                 (public member function)
         Inherited from std::ranges::view_interface
   empty returns whether the derived view is empty. Provided if it satisfies
   (C++20) sized_range or forward_range.
                 (public member function of std::ranges::view_interface<D>)
   cbegin returns a constant iterator to the beginning of the range.
   (C++23) (public member function of std::ranges::view_interface<D>)
   cend returns a sentinel for the constant iterator of the range.
   (C++23) (public member function of std::ranges::view_interface<D>)
   operator bool returns whether the derived view is not empty. Provided if
   (C++20) ranges::empty is applicable to it.
                 (public member function of std::ranges::view_interface<D>)
   front returns the first element in the derived view. Provided if it
   (C++20) satisfies forward_range.
                 (public member function of std::ranges::view_interface<D>)
   back returns the last element in the derived view. Provided if it satisfies
   (C++20) bidirectional_range and common_range.
                 (public member function of std::ranges::view_interface<D>)
   operator[] returns the n^th element in the derived view. Provided if it satisfies
   (C++20) random_access_range.
                 (public member function of std::ranges::view_interface<D>)
   Deduction guides
   (none)
   Nested classes
   iterator the iterator type
   (C++23) (exposition-only member class template*)
   sentinel the sentinel type used when adjacent_view is not a common_range
   (C++23) (exposition-only member class template*)
   Helper templates
   template< class V, size_t N >
   inline constexpr bool ranges::enable_borrowed_range<adjacent_view<V, (since C++23)
   N>> =
       ranges::enable_borrowed_range<V>;
   This specialization of ranges::enable_borrowed_range makes adjacent_view satisfy
   borrowed_range when the underlying view satisfies it.

Notes
   There are similarities between ranges::adjacent_view and ranges::slide_view:
     * Both create a "sliding window" of size N.
     * Both have the same size S - N + 1, where S is the size of an adapted view such
       that S >= N > 0.
   The differences between these adapters are:
                  View adaptor value_type The window size N
              ranges::adjacent_view A std::tuple object A template parameter
              ranges::slide_view A range A runtime parameter
    Feature-test macro Value Std Feature
                        std::ranges::zip_view,
   __cpp_lib_ranges_zip 202110L (C++23) std::ranges::zip_transform_view,
                        std::ranges::adjacent_view,
                        std::ranges::adjacent_transform_view

Example
// Run this code
 #include <array>
 #include <format>
 #include <iostream>
 #include <ranges>
 #include <tuple>
 int main()
 {
     constexpr std::array v{1, 2, 3, 4, 5, 6};
     std::cout << "v = [1 2 3 4 5 6]\n";
     for (int i{}; std::tuple t : v | std::views::adjacent<3>)
     {
         auto [t0, t1, t2] = t;
         std::cout << std::format("e = {:<{}}[{} {} {}]\n", "", 2 * i++, t0, t1, t2);
     }
 }

Output:
 v = [1 2 3 4 5 6]
 e = [1 2 3]
 e = [2 3 4]
 e = [3 4 5]
 e = [4 5 6]

References
     * C++23 standard (ISO/IEC 14882:2023):
     * 26.7.25 Adjacent view [range.adjacent]

See also
   ranges::adjacent_transform_view a view consisting of tuples of results of
   views::adjacent_transform application of a transformation function to adjacent
   (C++23) elements of the adapted view
                        (class template) (range adaptor object)
   ranges::slide_view a view whose M^th element is a view over the M^th
   views::slide through (M + N - 1)^th elements of another view
   (C++23) (class template) (range adaptor object)
   ranges::chunk_view a range of views that are N-sized non-overlapping
   views::chunk successive chunks of the elements of another view
   (C++23) (class template) (range adaptor object)
   ranges::stride_view a view consisting of elements of another view,
   views::stride advancing over N elements at a time
   (C++23) (class template) (range adaptor object)