cppdraft_translate/cppdraft/range/reverse.md

[range.reverse]

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]

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

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The name views​::​reverse denotes a range adaptor object ([range.adaptor.object]).

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

• (2.1)

  If the type of E is a (possibly cv-qualified) specialization of reverse_view, then E.base().

• (2.2)

  Otherwise, if the type of E is cv subrange<reverse_iterator, reverse_iterator, K> for some iterator type I and value K of type subrange_kind,

  • (2.2.1)

if K is subrange_kind​::​sized, thensubrange<I, I, K>(E.end().base(), E.begin().base(), E.size());

• (2.2.2)

otherwise, subrange<I, I, K>(E.end().base(), E.begin().base()).

However, in either case E is evaluated only once.

• (2.3)

  Otherwise, reverse_view{E}.

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[Example 1: vector is {0,1,2,3,4};for (int i : is | views::reverse) cout << i << ' '; // prints 4 3 2 1 0 — end example]

25.7.21.2 Class template reverse_view [range.reverse.view]

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

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constexpr explicit reverse_view(V base);

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

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

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

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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.

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constexpr reverse_iterator<iterator_t<V>> begin() requires [common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<V>; constexpr auto begin() const requires [common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<const V>;

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

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constexpr reverse_iterator<iterator_t<V>> end(); constexpr auto end() const requires [common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<const V>;

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