std::ranges::view::reverse, std::ranges::reverse_view

template< View V > requires BidirectionalRange<V> class reverse_view : public ranges::view_interface<reverse_view<V>>	(1)	(since C++20)
namespace view { inline constexpr /unspecified/ reverse = /unspecified/; }	(2)	(since C++20)

1) A range adaptor that represents a view of underlying View with reversed order.

2) The expression view::reverse(E) is expression-equivalent to (has the same effect as) one of the following expressions, except that E is evaluated only once:

E.base(), if the type of E is a (possibly cv-qualified) specialization of reverse_view;
otherwise, if the type of E is (possibly cv-qualified) ranges::subrange<std::reverse_iterator<I>, std::reverse_iterator<I>, K> for some iterator type I and value K of type ranges::subrange_kind:

ranges::subrange<I, I, K>(E.end().base(), E.begin().base(), E.size()), if K is ranges::subrange_kind::sized;
otherwise ranges::subrange<I, I, K>(E.end().base(), E.begin().base());

otherwise ranges::reverse_view{E}.

In other words, view::reverse unwraps reversed views if possible.

Data members

std::ranges::reverse_view::base_

V base_ = V(); /* exposition-only */

the underlying view

Member functions

std::ranges::reverse_view::reverse_view

reverse_view() = default;	(1)
constexpr reverse_view(V base);	(2)
template<ViewableRange R> requires BidirectionalRange<R> && Constructible<V, all_view<R>> constexpr reverse_view(R&& r);	(3)

1) Value-initializes base_

2) Initializes base_ with std::move(base).

3) Initializes base_ with view::all(std::forward<R>(r)).

Parameters

r

-

range to reverse

std::ranges::reverse_view::base

constexpr V base() const;

Equivalent to return base_;

std::ranges::reverse_view::begin

constexpr std::reverse_iterator<ranges::iterator_t<V>> begin();	(1)
constexpr std::reverse_iterator<ranges::iterator_t<V>> begin() requires CommonRange<V>;	(2)
constexpr std::reverse_iterator<ranges::iterator_t<const V>> begin() const requires CommonRange<const V>;	(2)

1) Returns std::make_reverse_iterator(ranges::next(ranges::begin(base_), ranges::end(base_))). In order to provide the amortized constant time complexity required by the Range concept, this function caches the result within the reverse_view object for use on subsequent calls.

2) Equivalent to return std::make_reverse_iterator(ranges::end(base_));.

std::ranges::reverse_view::end

constexpr std::reverse_iterator<ranges::iterator_t<V>> end() requires CommonRange<V>;
constexpr std::reverse_iterator<ranges::iterator_t<const V>> end() const requires CommonRange<const V>;

Equivalent to return std::make_reverse_iterator(ranges::begin(base_));.

std::ranges::reverse_view::size

constexpr auto size() requires SizedRange<V> { return ranges::size(base_); }
constexpr auto size() const requires SizedRange<const V> { return ranges::size(base_); }

Returns the size of the view if the view is bounded.

Deduction guides

template<class R> reverse_view(R&&) -> reverse_view<all_view<R>>;

Example

Run this code

#include <array>
#include <ranges>
#include <iostream>
 
int main()
{
    std::array<int, 6> il {3, 1, 4, 1, 5, 9};
    std::ranges::reverse_view rv {il};
    for (int i : rv)
        std::cout << i << ' ';
}

Output:

9 5 1 4 1 3

Language
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Language support library
Concepts library (C++20)
Diagnostics library
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