115 lines
6.3 KiB
Markdown
115 lines
6.3 KiB
Markdown
[range.reverse]
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# 25 Ranges library [[ranges]](./#ranges)
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## 25.7 Range adaptors [[range.adaptors]](range.adaptors#range.reverse)
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### 25.7.21 Reverse view [range.reverse]
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#### [25.7.21.1](#overview) Overview [[range.reverse.overview]](range.reverse.overview)
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[1](#overview-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9881)
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reverse_view takes a bidirectional view and produces
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another view that iterates the same elements in reverse order[.](#overview-1.sentence-1)
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[2](#overview-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9885)
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The name views::reverse denotes a
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range adaptor object ([[range.adaptor.object]](range.adaptor.object "25.7.2 Range adaptor objects"))[.](#overview-2.sentence-1)
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Given a subexpression E, the expressionviews::reverse(E) is expression-equivalent to:
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- [(2.1)](#overview-2.1)
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If the type of E is
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a (possibly cv-qualified) specialization of reverse_view,
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then E.base()[.](#overview-2.1.sentence-1)
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- [(2.2)](#overview-2.2)
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Otherwise, if the type of E is cv subrange<reverse_iterator<I>, reverse_iterator<I>, K> for some iterator type I and
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value K of type subrange_kind,
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* [(2.2.1)](#overview-2.2.1)
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if K is subrange_kind::sized, thensubrange<I, I, K>(E.end().base(), E.begin().base(), E.size());
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* [(2.2.2)](#overview-2.2.2)
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otherwise, subrange<I, I, K>(E.end().base(), E.begin().base())[.](#overview-2.2.sentence-1)
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However, in either case E is evaluated only once[.](#overview-2.2.sentence-2)
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- [(2.3)](#overview-2.3)
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Otherwise, reverse_view{E}[.](#overview-2.3.sentence-1)
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[3](#overview-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9912)
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[*Example [1](#overview-example-1)*: vector<int> is {0,1,2,3,4};for (int i : is | views::reverse) cout << i << ' '; // prints 4 3 2 1 0 â *end example*]
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#### [25.7.21.2](#view) Class template reverse_view [[range.reverse.view]](range.reverse.view)
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[ð](#lib:reverse_view)
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namespace std::ranges {template<[view](range.view#concept:view "25.4.5 Views [range.view]") V>requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<V>class reverse_view : public view_interface<reverse_view<V>> {private: V *base_* = V(); // *exposition only*public: reverse_view() requires [default_initializable](concept.default.init#concept:default_initializable "18.4.12 Concept default_initializable [concept.default.init]")<V> = default; constexpr explicit reverse_view(V r); constexpr V base() const & requires [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_constructible [concept.copyconstructible]")<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](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>; 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>; constexpr auto size() requires [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<V> {return ranges::size(*base_*); }constexpr auto size() const requires [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<const V> {return ranges::size(*base_*); }constexpr auto reserve_hint() requires [approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]")<V> {return ranges::reserve_hint(*base_*); }constexpr auto reserve_hint() const requires [approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]")<const V> {return ranges::reserve_hint(*base_*); }}; template<class R> reverse_view(R&&) -> reverse_view<views::all_t<R>>;}
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[ð](#lib:reverse_view,constructor)
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`constexpr explicit reverse_view(V base);
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`
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[1](#view-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9976)
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*Effects*: Initializes *base_* with std::move(base)[.](#view-1.sentence-1)
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[ð](#lib:begin,reverse_view)
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`constexpr reverse_iterator<iterator_t<V>> begin();
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`
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[2](#view-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9987)
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*Returns*: make_reverse_iterator(ranges::next(ranges::begin(*base_*), ranges::end(*base_*)))
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[3](#view-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9993)
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*Remarks*: In order to provide the amortized constant time complexity required by
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the [range](range.range#concept:range "25.4.2 Ranges [range.range]") concept, this function caches the result within thereverse_view for use on subsequent calls[.](#view-3.sentence-1)
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[ð](#lib:begin,reverse_view_)
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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>;
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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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`
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[4](#view-4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10007)
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*Effects*: Equivalent to: return make_reverse_iterator(ranges::end(*base_*));
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[ð](#lib:end,reverse_view)
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`constexpr reverse_iterator<iterator_t<V>> end();
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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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`
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[5](#view-5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10019)
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*Effects*: Equivalent to: return make_reverse_iterator(ranges::begin(*base_*));
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