std::ranges::views::slide, std::ranges::slide_view

< cpp‎ | ranges

Defined in header `<ranges>`
template< ranges::forward_range V > requires ranges::view<V> class slide_view : public ranges::view_interface<slide_view<V>>	(1)	(since C++23)
namespace views { inline constexpr /* unspecified / slide = / unspecified */; }	(2)	(since C++23)
Call signature
template< ranges::viewable_range R > constexpr ranges::view auto slide( R&& r, ranges::range_difference_t<R> n );		(since C++23)
template< class DifferenceType > constexpr /* range adaptor object */ slide( DifferenceType&& n );		(since C++23)
Helper concepts
template< class V > concept __slide_caches_nothing = ranges::random_access_range<V> && ranges::sized_range<V>;	(3)	(exposition only*)
template< class V > concept __slide_caches_last = !__slide_caches_nothing<V> && ranges::bidirectional_range<V> && ranges::common_range<V>;	(4)	(exposition only*)
template< class V > concept __slide_caches_first = !__slide_caches_nothing<V> && !__slide_caches_last<V>;	(5)	(exposition only*)

1) slide_view is a range adaptor that takes a view and a number n and produces a view whose m ^th element (a "window") is a view over the m ^th through (m + n - 1) ^th elements of the original view.

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::slide denotes a RangeAdaptorObject. Given subexpressions e and n, the expression views::slide(e, n) is expression-equivalent to slide_view(e, n).

If n is not greater than 0, the behavior is undefined.

slide_view always models forward_range, and models bidirectional_range, random_access_range, or sized_range if adapted view type models the corresponding concept.

Data members

Typical implementations of slide_view hold from two to four non-static data members:

the underlying view of type V (shown here as base_ for exposition only),
the "window size" of type ranges::range_difference_t<V> (shown here as n_ for exposition only).
the std::optional-like object (shown here as cached_begin_ for exposition only). May be present only if V models the __slide_caches_first helper concept (4).
the std::optional-like object (shown here as cached_end_ for exposition only). May be present only if V models the __slide_caches_last helper concept (5).

Member functions

(constructor) (C++23)	constructs a `slide_view` (public member function)
begin (C++23)	returns an iterator to the beginning (public member function)
end (C++23)	returns an iterator or a sentinel to the end (public member function)
size (C++23)	returns the number of elements. Provided only if the underlying (adapted) range satisfies `sized_range`. (public member function)
Inherited from std::ranges::view_interface
empty (C++20)	returns whether the derived view is empty. Provided if it satisfies `sized_range` or `forward_range`. (public member function of `std::ranges::view_interface<D>`)
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function of `std::ranges::view_interface<D>`)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function of `std::ranges::view_interface<D>`)
operator bool (C++20)	returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of `std::ranges::view_interface<D>`)
front (C++20)	returns the first element in the derived view. Provided if it satisfies `forward_range`. (public member function of `std::ranges::view_interface<D>`)
back (C++20)	returns the last element in the derived view. Provided if it satisfies `bidirectional_range` and `common_range`. (public member function of `std::ranges::view_interface<D>`)
operator[] (C++20)	returns the n^th element in the derived view. Provided if it satisfies `random_access_range`. (public member function of `std::ranges::view_interface<D>`)

Deduction guides

Nested classes

iterator (C++23)	the iterator type (exposition-only member class template*)
sentinel (C++23)	the sentinel type used when `slide_view` is not a `common_range` (exposition-only member class template*)

Helper templates

template< class V > inline constexpr bool ranges::enable_borrowed_range<slide_view<V>> = ranges::enable_borrowed_range<V>;		(since C++23)

This specialization of ranges::enable_borrowed_range makes slide_view satisfy borrowed_range when the underlying view satisfies it.

Notes

There is a similarity between ranges::adjacent_view and ranges::slide_view — they both produce a "sliding window" of the size N, and, given a view of the size S, where S >= N > 0, they both will have the same size: S - N + 1. The difference between these view adaptors are:

View adaptor	`value_type`	The window size `N`
ranges::adjacent_view	a tuple-like object	a template parameter
ranges::slide_view	a `range`	a runtime parameter

Feature-test macro	Value	Std	Comment
`__cpp_lib_ranges_slide`	202202L	(C++23)	`std::ranges::slide_view`

Example

#include <algorithm>
#include <iostream>
#include <ranges>
 
auto print_subrange = [](std::ranges::viewable_range auto&& r)
{
    std::cout << '[';
    for (int pos{}; auto elem : r)
        std::cout << (pos++ ? " " : "") << elem;
    std::cout << "] ";
};
 
int main()
{
    const auto v = {1, 2, 3, 4, 5, 6};
 
    std::cout << "All sliding windows of width:\n";
    for (const unsigned width : std::views::iota(1U, 1U + v.size()))
    {
        auto const windows = v | std::views::slide(width);
        std::cout << "W = " << width << ": ";
        std::ranges::for_each(windows, print_subrange);
        std::cout << '\n';
    }
}

Output:

All sliding windows of width W:
W = 1: [1] [2] [3] [4] [5] [6] 
W = 2: [1 2] [2 3] [3 4] [4 5] [5 6] 
W = 3: [1 2 3] [2 3 4] [3 4 5] [4 5 6] 
W = 4: [1 2 3 4] [2 3 4 5] [3 4 5 6] 
W = 5: [1 2 3 4 5] [2 3 4 5 6] 
W = 6: [1 2 3 4 5 6]

References

C++23 standard (ISO/IEC 14882:2023):

26.7.29 Slide view [range.slide]

ranges::adjacent_viewviews::adjacent (C++23)	a `view` consisting of tuples of references to adjacent elements of the adapted view (class template) (range adaptor object)
ranges::chunk_viewviews::chunk (C++23)	a range of `view`s that are `N`-sized non-overlapping successive chunks of the elements of another `view` (class template) (range adaptor object)