92 lines
3.8 KiB
Markdown
92 lines
3.8 KiB
Markdown
[range.take.overview]
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# 25 Ranges library [[ranges]](./#ranges)
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## 25.7 Range adaptors [[range.adaptors]](range.adaptors#range.take.overview)
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### 25.7.10 Take view [[range.take]](range.take#overview)
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#### 25.7.10.1 Overview [range.take.overview]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L5864)
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take_view produces a view of the first N elements
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from another view, or all the elements if the adapted
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view contains fewer than N[.](#1.sentence-1)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L5869)
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The name views::take denotes a
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range adaptor object ([[range.adaptor.object]](range.adaptor.object "25.7.2 Range adaptor objects"))[.](#2.sentence-1)
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Let E and F be expressions,
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let T be remove_cvref_t<decltype((E))>, and
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let D be range_difference_t<decltype((E))>[.](#2.sentence-2)
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If decltype((F)) does not model[convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_to [concept.convertible]")<D>,views::take(E, F) is ill-formed[.](#2.sentence-3)
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Otherwise, the expression views::take(E, F) is expression-equivalent to:
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- [(2.1)](#2.1)
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If T is a specialization
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of empty_view ([[range.empty.view]](range.empty.view "25.6.2.2 Class template empty_view")),
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then ((void)F, *decay-copy*(E)),
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except that the evaluations of E and F are indeterminately sequenced[.](#2.1.sentence-1)
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- [(2.2)](#2.2)
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Otherwise, if T models[random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]") and [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]") and is a specialization ofspan ([[views.span]](views.span "23.7.2.2 Class template span")),basic_string_view ([[string.view]](string.view "27.3 String view classes")), orsubrange ([[range.subrange]](range.subrange "25.5.4 Sub-ranges")),
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thenU(ranges::begin(E),
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ranges::begin(E) + std::min<D>(ranges::distance(E), F)),
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except that E is evaluated only once,
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where U is a type determined as follows:
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* [(2.2.1)](#2.2.1)
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if T is a specialization of span,
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then U is span<typename T::element_type>;
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* [(2.2.2)](#2.2.2)
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otherwise, if T is a specialization of basic_string_view,
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then U is T;
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* [(2.2.3)](#2.2.3)
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otherwise, T is a specialization of subrange, andU is subrange<iterator_t<T>>;
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- [(2.3)](#2.3)
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otherwise, if T is
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a specialization of iota_view ([[range.iota.view]](range.iota.view "25.6.4.2 Class template iota_view"))
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that models [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]") and [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]"),
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theniota_view(*ranges::begin(E),*(ranges::begin(E) + std::min<D>(ranges::distance(E), F))),
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except that E is evaluated only once[.](#2.3.sentence-1)
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- [(2.4)](#2.4)
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Otherwise, if T is
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a specialization of repeat_view ([[range.repeat.view]](range.repeat.view "25.6.5.2 Class template repeat_view")):
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* [(2.4.1)](#2.4.1)
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if T models [sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]"),
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thenviews::repeat(*E.*value_*, std::min<D>(ranges::distance(E), F)) except that E is evaluated only once;
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* [(2.4.2)](#2.4.2)
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otherwise, views::repeat(*E.*value_*, static_cast<D>(F))[.](#2.4.sentence-1)
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- [(2.5)](#2.5)
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Otherwise, take_view(E, F)[.](#2.5.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L5938)
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[*Example [1](#example-1)*: vector<int> is{0,1,2,3,4,5,6,7,8,9};for (int i : is | views::take(5)) cout << i << ' '; // prints 0 1 2 3 4 â *end example*]
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