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[range.elements]
# 25 Ranges library [[ranges]](./#ranges)
## 25.7 Range adaptors [[range.adaptors]](range.adaptors#range.elements)
### 25.7.23 Elements view [range.elements]
#### [25.7.23.1](#overview) Overview [[range.elements.overview]](range.elements.overview)
[1](#overview-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10131)
elements_view takes
a view of tuple-like values and a size_t, and
produces a view with a value-type of the Nth element
of the adapted view's value-type[.](#overview-1.sentence-1)
[2](#overview-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10137)
The name views​::​elements<N> denotes
a range adaptor object ([[range.adaptor.object]](range.adaptor.object "25.7.2 Range adaptor objects"))[.](#overview-2.sentence-1)
Given a subexpression E and constant expression N,
the expression views​::​elements<N>(E) is expression-equivalent toelements_view<views​::​all_t<decltype((E))>, N>{E}[.](#overview-2.sentence-2)
[*Example [1](#overview-example-1)*: auto historical_figures = map{ pair{"Lovelace"sv, 1815}, {"Turing"sv, 1912}, {"Babbage"sv, 1791}, {"Hamilton"sv, 1936}};
auto names = historical_figures | views::elements<0>;for (auto&& name : names) { cout << name << ' '; // prints Babbage Hamilton Lovelace Turing }auto birth_years = historical_figures | views::elements<1>;for (auto&& born : birth_years) { cout << born << ' '; // prints 1791 1936 1815 1912 } — *end example*]
[3](#overview-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10166)
keys_view is an alias for elements_view<R, 0>, and
is useful for extracting keys from associative containers[.](#overview-3.sentence-1)
[*Example [2](#overview-example-2)*: auto names = historical_figures | views::keys;for (auto&& name : names) { cout << name << ' '; // prints Babbage Hamilton Lovelace Turing } — *end example*]
[4](#overview-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10179)
values_view is an alias for elements_view<R, 1>, and
is useful for extracting values from associative containers[.](#overview-4.sentence-1)
[*Example [3](#overview-example-3)*: auto is_even = [](const auto x) { return x % 2 == 0; };
cout << ranges::count_if(historical_figures | views::values, is_even); // prints 2 — *end example*]
#### [25.7.23.2](#view) Class template elements_view [[range.elements.view]](range.elements.view)
[🔗](#lib:elements_view)
namespace std::ranges {template<class T, size_t N>concept [*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]") = // *exposition only*[*tuple-like*](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]")<T> && N < tuple_size_v<T>; template<class T, size_t N>concept [*returnable-element*](#concept:returnable-element "25.7.23.2 Class template elements_­view [range.elements.view]") = // *exposition only* is_reference_v<T> || [move_constructible](concept.moveconstructible#concept:move_constructible "18.4.13 Concept move_­constructible [concept.moveconstructible]")<tuple_element_t<N, T>>; template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") V, size_t N>requires [view](range.view#concept:view "25.4.5 Views [range.view]")<V> && [*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_value_t<V>, N> &&[*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<remove_reference_t<range_reference_t<V>>, N> &&[*returnable-element*](#concept:returnable-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_reference_t<V>, N>class elements_view : public view_interface<elements_view<V, N>> {public: elements_view() requires [default_initializable](concept.default.init#concept:default_initializable "18.4.12 Concept default_­initializable [concept.default.init]")<V> = default; constexpr explicit elements_view(V base); 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 auto begin() requires (![*simple-view*](range.utility.helpers#concept:simple-view "25.5.2 Helper concepts [range.utility.helpers]")<V>){ return *iterator*<false>(ranges::begin(*base_*)); }constexpr auto begin() const requires [range](range.range#concept:range "25.4.2 Ranges [range.range]")<const V>{ return *iterator*<true>(ranges::begin(*base_*)); }constexpr auto end() requires (![*simple-view*](range.utility.helpers#concept:simple-view "25.5.2 Helper concepts [range.utility.helpers]")<V> && ![common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<V>){ return *sentinel*<false>{ranges::end(*base_*)}; }constexpr auto end() requires (![*simple-view*](range.utility.helpers#concept:simple-view "25.5.2 Helper concepts [range.utility.helpers]")<V> && [common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<V>){ return *iterator*<false>{ranges::end(*base_*)}; }constexpr auto end() const requires [range](range.range#concept:range "25.4.2 Ranges [range.range]")<const V>{ return *sentinel*<true>{ranges::end(*base_*)}; }constexpr auto end() const requires [common_range](range.refinements#concept:common_range "25.4.6 Other range refinements [range.refinements]")<const V>{ return *iterator*<true>{ranges::end(*base_*)}; }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_*); }private:// [[range.elements.iterator]](#iterator "25.7.23.3 Class template elements_­view​::​iterator"), class template elements_view​::​*iterator*template<bool> class *iterator*; // *exposition only*// [[range.elements.sentinel]](#sentinel "25.7.23.4 Class template elements_­view​::​sentinel"), class template elements_view​::​*sentinel*template<bool> class *sentinel*; // *exposition only* V *base_* = V(); // *exposition only*};}
[🔗](#lib:elements_view,constructor)
`constexpr explicit elements_view(V base);
`
[1](#view-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10267)
*Effects*: Initializes *base_* with std​::​move(base)[.](#view-1.sentence-1)
#### [25.7.23.3](#iterator) Class template elements_view​::​*iterator* [[range.elements.iterator]](range.elements.iterator)
[🔗](#lib:elements_view::iterator)
namespace std::ranges {template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") V, size_t N>requires [view](range.view#concept:view "25.4.5 Views [range.view]")<V> && [*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_value_t<V>, N> &&[*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<remove_reference_t<range_reference_t<V>>, N> &&[*returnable-element*](#concept:returnable-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_reference_t<V>, N>template<bool Const>class elements_view<V, N>::*iterator* {using *Base* = *maybe-const*<Const, V>; // *exposition only* iterator_t<*Base*> *current_* = iterator_t<*Base*>(); // *exposition only*static constexpr decltype(auto) *get-element*(const iterator_t<*Base*>& i); // *exposition only*public:using iterator_concept = *see below*; using iterator_category = *see below*; // not always presentusing value_type = remove_cvref_t<tuple_element_t<N, range_value_t<*Base*>>>; using difference_type = range_difference_t<*Base*>; *iterator*() requires [default_initializable](concept.default.init#concept:default_initializable "18.4.12 Concept default_­initializable [concept.default.init]")<iterator_t<*Base*>> = default; constexpr explicit *iterator*(iterator_t<*Base*> current); constexpr *iterator*(*iterator*<!Const> i)requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<iterator_t<V>, iterator_t<*Base*>>; constexpr const iterator_t<*Base*>& base() const & noexcept; constexpr iterator_t<*Base*> base() &&; constexpr decltype(auto) operator*() const{ return *get-element*(*current_*); }constexpr *iterator*& operator++(); constexpr void operator++(int); constexpr *iterator* operator++(int) requires [forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; constexpr *iterator*& operator--() requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; constexpr *iterator* operator--(int) requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; constexpr *iterator*& operator+=(difference_type x)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; constexpr *iterator*& operator-=(difference_type x)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; constexpr decltype(auto) operator[](difference_type n) constrequires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>{ return *get-element*(*current_* + n); }friend constexpr bool operator==(const *iterator*& x, const *iterator*& y)requires [equality_comparable](concept.equalitycomparable#concept:equality_comparable "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<iterator_t<*Base*>>; friend constexpr bool operator<(const *iterator*& x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr bool operator>(const *iterator*& x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr bool operator<=(const *iterator*& x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr bool operator>=(const *iterator*& x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr auto operator<=>(const *iterator*& x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<iterator_t<*Base*>>; friend constexpr *iterator* operator+(const *iterator*& x, difference_type y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr *iterator* operator+(difference_type x, const *iterator*& y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr *iterator* operator-(const *iterator*& x, difference_type y)requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<*Base*>; friend constexpr difference_type operator-(const *iterator*& x, const *iterator*& y)requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<iterator_t<*Base*>, iterator_t<*Base*>>; };}
[1](#iterator-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10348)
The member [*typedef-name*](dcl.typedef#nt:typedef-name "9.2.4 The typedef specifier [dcl.typedef]") iterator_concept is defined as follows:
- [(1.1)](#iterator-1.1)
If *Base* models [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]"),
then iterator_concept denotes random_access_iterator_tag[.](#iterator-1.1.sentence-1)
- [(1.2)](#iterator-1.2)
Otherwise, if *Base* models [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]"),
then iterator_concept denotes bidirectional_iterator_tag[.](#iterator-1.2.sentence-1)
- [(1.3)](#iterator-1.3)
Otherwise, if *Base* models [forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]"),
then iterator_concept denotes forward_iterator_tag[.](#iterator-1.3.sentence-1)
- [(1.4)](#iterator-1.4)
Otherwise, iterator_concept denotes input_iterator_tag[.](#iterator-1.4.sentence-1)
[2](#iterator-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10365)
The member [*typedef-name*](dcl.typedef#nt:typedef-name "9.2.4 The typedef specifier [dcl.typedef]") iterator_category is defined
if and only if *Base* models [forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")[.](#iterator-2.sentence-1)
In that case, iterator_category is defined as follows:
Let C denote the typeiterator_traits<iterator_t<*Base*>>​::​iterator_category[.](#iterator-2.sentence-2)
- [(2.1)](#iterator-2.1)
If std​::​get<N>(**current_*) is an rvalue,iterator_category denotes input_iterator_tag[.](#iterator-2.1.sentence-1)
- [(2.2)](#iterator-2.2)
Otherwise, if C models [derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<random_access_iterator_tag>,iterator_category denotes random_access_iterator_tag[.](#iterator-2.2.sentence-1)
- [(2.3)](#iterator-2.3)
Otherwise, iterator_category denotes C[.](#iterator-2.3.sentence-1)
[🔗](#lib:get-element,elements_view::iterator)
`static constexpr decltype(auto) get-element(const iterator_t<Base>& i);
`
[3](#iterator-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10388)
*Effects*: Equivalent to:if constexpr (is_reference_v<range_reference_t<*Base*>>) {return std::get<N>(*i);} else {using E = remove_cv_t<tuple_element_t<N, range_reference_t<*Base*>>>; return static_cast<E>(std::get<N>(*i));}
[🔗](#lib:elements_view::iterator,constructor)
`constexpr explicit iterator(iterator_t<Base> current);
`
[4](#iterator-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10407)
*Effects*: Initializes *current_* with std​::​move(current)[.](#iterator-4.sentence-1)
[🔗](#lib:elements_view::iterator,constructor_)
`constexpr iterator(iterator<!Const> i)
requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<iterator_t<V>, iterator_t<Base>>;
`
[5](#iterator-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10419)
*Effects*: Initializes *current_* with std​::​move(i.*current_*)[.](#iterator-5.sentence-1)
[🔗](#lib:base,elements_view::iterator)
`constexpr const iterator_t<Base>& base() const & noexcept;
`
[6](#iterator-6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10430)
*Effects*: Equivalent to: return *current_*;
[🔗](#lib:base,elements_view::iterator_)
`constexpr iterator_t<Base> base() &&;
`
[7](#iterator-7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10441)
*Effects*: Equivalent to: return std​::​move(*current_*);
[🔗](#lib:operator++,elements_view::iterator)
`constexpr iterator& operator++();
`
[8](#iterator-8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10452)
*Effects*: Equivalent to:++*current_*;return *this;
[🔗](#lib:operator++,elements_view::iterator_)
`constexpr void operator++(int);
`
[9](#iterator-9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10467)
*Effects*: Equivalent to: ++*current_*[.](#iterator-9.sentence-1)
[🔗](#lib:operator++,elements_view::iterator__)
`constexpr iterator operator++(int) requires [forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[10](#iterator-10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10478)
*Effects*: Equivalent to:auto temp = *this;++*current_*;return temp;
[🔗](#lib:operator--,elements_view::iterator)
`constexpr iterator& operator--() requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[11](#iterator-11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10494)
*Effects*: Equivalent to:--*current_*;return *this;
[🔗](#lib:operator--,elements_view::iterator_)
`constexpr iterator operator--(int) requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[12](#iterator-12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10509)
*Effects*: Equivalent to:auto temp = *this;--*current_*;return temp;
[🔗](#lib:operator+=,elements_view::iterator)
`constexpr iterator& operator+=(difference_type n)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[13](#iterator-13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10526)
*Effects*: Equivalent to:*current_* += n;return *this;
[🔗](#lib:operator-=,elements_view::iterator)
`constexpr iterator& operator-=(difference_type n)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[14](#iterator-14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10542)
*Effects*: Equivalent to:*current_* -= n;return *this;
[🔗](#lib:operator==,elements_view::iterator)
`friend constexpr bool operator==(const iterator& x, const iterator& y)
requires [equality_comparable](concept.equalitycomparable#concept:equality_comparable "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<Base>;
`
[15](#iterator-15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10558)
*Effects*: Equivalent to: return x.*current_* == y.*current_*;
[🔗](#lib:operator%3c,elements_view::iterator)
`friend constexpr bool operator<(const iterator& x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[16](#iterator-16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10570)
*Effects*: Equivalent to: return x.*current_* < y.*current_*;
[🔗](#lib:operator%3e,elements_view::iterator)
`friend constexpr bool operator>(const iterator& x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[17](#iterator-17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10582)
*Effects*: Equivalent to: return y < x;
[🔗](#lib:operator%3c=,elements_view::iterator)
`friend constexpr bool operator<=(const iterator& x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[18](#iterator-18)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10594)
*Effects*: Equivalent to: return !(y < x);
[🔗](#lib:operator%3e=,elements_view::iterator)
`friend constexpr bool operator>=(const iterator& x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[19](#iterator-19)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10606)
*Effects*: Equivalent to: return !(x < y);
[🔗](#lib:operator%3c=%3e,elements_view::iterator)
`friend constexpr auto operator<=>(const iterator& x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<iterator_t<Base>>;
`
[20](#iterator-20)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10618)
*Effects*: Equivalent to: return x.*current_* <=> y.*current_*;
[🔗](#lib:operator+,elements_view::iterator)
`friend constexpr iterator operator+(const iterator& x, difference_type y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[21](#iterator-21)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10630)
*Effects*: Equivalent to: return *iterator*{x} += y;
[🔗](#lib:operator+,elements_view::iterator_)
`friend constexpr iterator operator+(difference_type x, const iterator& y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[22](#iterator-22)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10642)
*Effects*: Equivalent to: return y + x;
[🔗](#lib:operator-,elements_view::iterator)
`friend constexpr iterator operator-(const iterator& x, difference_type y)
requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;
`
[23](#iterator-23)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10654)
*Effects*: Equivalent to: return *iterator*{x} -= y;
[🔗](#lib:operator-,elements_view::iterator_)
`friend constexpr difference_type operator-(const iterator& x, const iterator& y)
requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<iterator_t<Base>, iterator_t<Base>>;
`
[24](#iterator-24)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10666)
*Effects*: Equivalent to: return x.*current_* - y.*current_*;
#### [25.7.23.4](#sentinel) Class template elements_view​::​*sentinel* [[range.elements.sentinel]](range.elements.sentinel)
[🔗](#lib:elements_view::sentinel)
namespace std::ranges {template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") V, size_t N>requires [view](range.view#concept:view "25.4.5 Views [range.view]")<V> && [*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_value_t<V>, N> &&[*has-tuple-element*](#concept:has-tuple-element "25.7.23.2 Class template elements_­view [range.elements.view]")<remove_reference_t<range_reference_t<V>>, N> &&[*returnable-element*](#concept:returnable-element "25.7.23.2 Class template elements_­view [range.elements.view]")<range_reference_t<V>, N>template<bool Const>class elements_view<V, N>::*sentinel* {private:using *Base* = *maybe-const*<Const, V>; // *exposition only* sentinel_t<*Base*> *end_* = sentinel_t<*Base*>(); // *exposition only*public:*sentinel*() = default; constexpr explicit *sentinel*(sentinel_t<*Base*> end); constexpr *sentinel*(*sentinel*<!Const> other)requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<sentinel_t<V>, sentinel_t<*Base*>>; constexpr sentinel_t<*Base*> base() const; template<bool OtherConst>requires [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<sentinel_t<*Base*>, iterator_t<*maybe-const*<OtherConst, V>>>friend constexpr bool operator==(const *iterator*<OtherConst>& x, const *sentinel*& y); template<bool OtherConst>requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<*Base*>, iterator_t<*maybe-const*<OtherConst, V>>>friend constexpr range_difference_t<*maybe-const*<OtherConst, V>>operator-(const *iterator*<OtherConst>& x, const *sentinel*& y); template<bool OtherConst>requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<*Base*>, iterator_t<*maybe-const*<OtherConst, V>>>friend constexpr range_difference_t<*maybe-const*<OtherConst, V>>operator-(const *sentinel*& x, const *iterator*<OtherConst>& y); };}
[🔗](#lib:elements_view::sentinel,constructor)
`constexpr explicit sentinel(sentinel_t<Base> end);
`
[1](#sentinel-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10717)
*Effects*: Initializes *end_* with end[.](#sentinel-1.sentence-1)
[🔗](#lib:elements_view::sentinel,constructor_)
`constexpr sentinel(sentinel<!Const> other)
requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<sentinel_t<V>, sentinel_t<Base>>;
`
[2](#sentinel-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10729)
*Effects*: Initializes *end_* with std​::​move(other.*end_*)[.](#sentinel-2.sentence-1)
[🔗](#lib:base,elements_view::sentinel)
`constexpr sentinel_t<Base> base() const;
`
[3](#sentinel-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10740)
*Effects*: Equivalent to: return *end_*;
[🔗](#lib:operator==,elements_view::sentinel)
`template<bool OtherConst>
requires [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);
`
[4](#sentinel-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10753)
*Effects*: Equivalent to: return x.*current_* == y.*end_*;
[🔗](#lib:operator-,elements_view::sentinel)
`template<bool OtherConst>
requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr range_difference_t<maybe-const<OtherConst, V>>
operator-(const iterator<OtherConst>& x, const sentinel& y);
`
[5](#sentinel-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10767)
*Effects*: Equivalent to: return x.*current_* - y.*end_*;
[🔗](#lib:operator-,elements_view::sentinel_)
`template<bool OtherConst>
requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<Base>, iterator_t<maybe-const<OtherConst, V>>>
friend constexpr range_difference_t<maybe-const<OtherConst, V>>
operator-(const sentinel& x, const iterator<OtherConst>& y);
`
[6](#sentinel-6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L10781)
*Effects*: Equivalent to: return x.*end_* - y.*current_*;
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