[range.reverse] (original) (raw)

25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.21 Reverse view [range.reverse]

25.7.21.1 Overview [range.reverse.overview]

reverse_view takes a bidirectional view and produces another view that iterates the same elements in reverse order.

Given a subexpression E, the expressionviews​::​reverse(E) is expression-equivalent to:

• If the type of E is a (possibly cv-qualified) specialization of reverse_view, then E.base().
• Otherwise, if the type of E is cv subrange<reverse_iterator<I>, reverse_iterator<I>, K> for some iterator type I and value K of type subrange_kind,
  • if K is subrange_kind​::​sized, thensubrange<I, I, K>(E.end().base(), E.begin().base(), E.size());
  • otherwise, subrange<I, I, K>(E.end().base(), E.begin().base()).
    However, in either case E is evaluated only once.
• Otherwise, reverse_view{E}.

[Example 1: vector<int> is {0,1,2,3,4};for (int i : is | views::reverse) cout << i << ' '; — _end example_]

25.7.21.2 Class template reverse_view [range.reverse.view]

namespace std::ranges { template<view V> requires bidirectional_range<V> class reverse_view : public view_interface<reverse_view<V>> { private: V base_ = V(); public: reverse_view() requires default_initializable<V> = default;constexpr explicit reverse_view(V r);constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr reverse_iterator<iterator_t<V>> begin();constexpr reverse_iterator<iterator_t<V>> begin() requires common_range<V>;constexpr auto begin() const requires common_range<const V>;constexpr reverse_iterator<iterator_t<V>> end();constexpr auto end() const requires common_range<const V>;constexpr auto size() requires sized_range<V> { return ranges::size(base_);} constexpr auto size() const requires sized_range<const V> { return ranges::size(base_);} constexpr auto reserve_hint() requires approximately_sized_range<V> { return ranges::reserve_hint(base_);} constexpr auto reserve_hint() const requires approximately_sized_range<const V> { return ranges::reserve_hint(base_);} };template<class R> reverse_view(R&&) -> reverse_view<views::all_t<R>>;}

constexpr explicit reverse_view(V base);

Effects: Initializes base_ with std​::​move(base).

constexpr reverse_iterator<iterator_t<V>> begin();

Returns: make_reverse_iterator(ranges::next(ranges::begin(base_), ranges::end(base_)))

Remarks: In order to provide the amortized constant time complexity required by the range concept, this function caches the result within thereverse_view for use on subsequent calls.

constexpr reverse_iterator<iterator_t<V>> begin() requires [common_range](range.refinements#concept:common%5Frange "25.4.5 Other range refinements [range.refinements]")<V>;constexpr auto begin() const requires [common_range](range.refinements#concept:common%5Frange "25.4.5 Other range refinements [range.refinements]")<const V>;

Effects: Equivalent to: return make_reverse_iterator(ranges​::​end(base_));

constexpr reverse_iterator<iterator_t<V>> end();constexpr auto end() const requires [common_range](range.refinements#concept:common%5Frange "25.4.5 Other range refinements [range.refinements]")<const V>;

Effects: Equivalent to: return make_reverse_iterator(ranges​::​begin(base_));