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[range.iota.iterator]
# 25 Ranges library [[ranges]](./#ranges)
## 25.6 Range factories [[range.factories]](range.factories#range.iota.iterator)
### 25.6.4 Iota view [[range.iota]](range.iota#iterator)
#### 25.6.4.3 Class iota_view​::​*iterator* [range.iota.iterator]
[🔗](#lib:iota_view::iterator)
namespace std::ranges {template<[weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") W, [semiregular](concepts.object#concept:semiregular "18.6 Object concepts [concepts.object]") Bound>requires [*weakly-equality-comparable-with*](concept.equalitycomparable#concept:weakly-equality-comparable-with "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<W, Bound> && [copyable](concepts.object#concept:copyable "18.6 Object concepts [concepts.object]")<W>struct iota_view<W, Bound>::*iterator* {private: W *value_* = W(); // *exposition only*public:using iterator_concept = *see below*; using iterator_category = input_iterator_tag; // present only if W models [incrementable](iterator.concept.inc#concept:incrementable "24.3.4.5 Concept incrementable [iterator.concept.inc]") and// *IOTA-DIFF-T*(W) is an integral typeusing value_type = W; using difference_type = *IOTA-DIFF-T*(W); *iterator*() requires [default_initializable](concept.default.init#concept:default_initializable "18.4.12 Concept default_­initializable [concept.default.init]")<W> = default; constexpr explicit *iterator*(W value); constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>); constexpr *iterator*& operator++(); constexpr void operator++(int); constexpr *iterator* operator++(int) requires [incrementable](iterator.concept.inc#concept:incrementable "24.3.4.5 Concept incrementable [iterator.concept.inc]")<W>; constexpr *iterator*& operator--() requires [*decrementable*](range.iota.view#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; constexpr *iterator* operator--(int) requires [*decrementable*](range.iota.view#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; constexpr *iterator*& operator+=(difference_type n)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; constexpr *iterator*& operator-=(difference_type n)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; constexpr W operator[](difference_type n) constrequires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; 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]")<W>; friend constexpr bool operator<(const *iterator*& x, const *iterator*& y)requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>; friend constexpr bool operator>(const *iterator*& x, const *iterator*& y)requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>; friend constexpr bool operator<=(const *iterator*& x, const *iterator*& y)requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>; friend constexpr bool operator>=(const *iterator*& x, const *iterator*& y)requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>; friend constexpr auto operator<=>(const *iterator*& x, const *iterator*& y)requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<W>; friend constexpr *iterator* operator+(*iterator* i, difference_type n)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; friend constexpr *iterator* operator+(difference_type n, *iterator* i)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; friend constexpr *iterator* operator-(*iterator* i, difference_type n)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; friend constexpr difference_type operator-(const *iterator*& x, const *iterator*& y)requires [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>; };}
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3167)
*iterator*​::​iterator_concept is defined as follows:
- [(1.1)](#1.1)
If W models [*advanceable*](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]"), theniterator_concept is random_access_iterator_tag[.](#1.1.sentence-1)
- [(1.2)](#1.2)
Otherwise, if W models [*decrementable*](range.iota.view#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]"), theniterator_concept is bidirectional_iterator_tag[.](#1.2.sentence-1)
- [(1.3)](#1.3)
Otherwise, if W models [incrementable](iterator.concept.inc#concept:incrementable "24.3.4.5 Concept incrementable [iterator.concept.inc]"), theniterator_concept is forward_iterator_tag[.](#1.3.sentence-1)
- [(1.4)](#1.4)
Otherwise, iterator_concept is input_iterator_tag[.](#1.4.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3179)
[*Note [1](#note-1)*:
Overloads for iter_move and iter_swap are omitted intentionally[.](#2.sentence-1)
— *end note*]
[🔗](#lib:iota_view::iterator,constructor)
`constexpr explicit iterator(W value);
`
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3190)
*Effects*: Initializes *value_* with value[.](#3.sentence-1)
[🔗](#lib:operator*,iota_view::iterator)
`constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);
`
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3201)
*Effects*: Equivalent to: return *value_*;
[5](#5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3205)
[*Note [2](#note-2)*:
The noexcept clause is needed by the default iter_move implementation[.](#5.sentence-1)
— *end note*]
[🔗](#lib:operator++,iota_view::iterator)
`constexpr iterator& operator++();
`
[6](#6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3218)
*Effects*: Equivalent to:++*value_*;return *this;
[🔗](#lib:operator++,iota_view::iterator_)
`constexpr void operator++(int);
`
[7](#7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3233)
*Effects*: Equivalent to ++*this[.](#7.sentence-1)
[🔗](#lib:operator++,iota_view::iterator__)
`constexpr iterator operator++(int) requires [incrementable](iterator.concept.inc#concept:incrementable "24.3.4.5 Concept incrementable [iterator.concept.inc]")<W>;
`
[8](#8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3244)
*Effects*: Equivalent to:auto tmp = *this;++*this;return tmp;
[🔗](#lib:operator--,iota_view::iterator)
`constexpr iterator& operator--() requires [decrementable](range.iota.view#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[9](#9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3260)
*Effects*: Equivalent to:--*value_*;return *this;
[🔗](#lib:operator--,iota_view::iterator_)
`constexpr iterator operator--(int) requires [decrementable](range.iota.view#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[10](#10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3275)
*Effects*: Equivalent to:auto tmp = *this;--*this;return tmp;
[🔗](#lib:operator+=,iota_view::iterator)
`constexpr iterator& operator+=(difference_type n)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[11](#11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3292)
*Effects*: Equivalent to:if constexpr (*is-integer-like*<W> && !*is-signed-integer-like*<W>) {if (n >= difference_type(0))*value_* += static_cast<W>(n); else*value_* -= static_cast<W>(-n);} else {*value_* += n;}return *this;
[🔗](#lib:operator-=,iota_view::iterator)
`constexpr iterator& operator-=(difference_type n)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[12](#12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3315)
*Effects*: Equivalent to:if constexpr (*is-integer-like*<W> && !*is-signed-integer-like*<W>) {if (n >= difference_type(0))*value_* -= static_cast<W>(n); else*value_* += static_cast<W>(-n);} else {*value_* -= n;}return *this;
[🔗](#lib:operator%5b%5d,iota_view::iterator)
`constexpr W operator[](difference_type n) const
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[13](#13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3338)
*Effects*: Equivalent to: return W(*value_* + n);
[🔗](#lib:operator==,iota_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]")<W>;
`
[14](#14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3350)
*Effects*: Equivalent to: return x.*value_* == y.*value_*;
[🔗](#lib:operator%3c,iota_view::iterator)
`friend constexpr bool operator<(const iterator& x, const iterator& y)
requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>;
`
[15](#15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3362)
*Effects*: Equivalent to: return x.*value_* < y.*value_*;
[🔗](#lib:operator%3e,iota_view::iterator)
`friend constexpr bool operator>(const iterator& x, const iterator& y)
requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>;
`
[16](#16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3374)
*Effects*: Equivalent to: return y < x;
[🔗](#lib:operator%3c=,iota_view::iterator)
`friend constexpr bool operator<=(const iterator& x, const iterator& y)
requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>;
`
[17](#17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3386)
*Effects*: Equivalent to: return !(y < x);
[🔗](#lib:operator%3e=,iota_view::iterator)
`friend constexpr bool operator>=(const iterator& x, const iterator& y)
requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W>;
`
[18](#18)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3398)
*Effects*: Equivalent to: return !(x < y);
[🔗](#lib:operator%3c=%3e,iota_view::iterator)
`friend constexpr auto operator<=>(const iterator& x, const iterator& y)
requires [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<W> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<W>;
`
[19](#19)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3410)
*Effects*: Equivalent to: return x.*value_* <=> y.*value_*;
[🔗](#lib:operator+,iota_view::iterator)
`friend constexpr iterator operator+(iterator i, difference_type n)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[20](#20)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3422)
*Effects*: Equivalent to:i += n;return i;
[🔗](#lib:operator+,iota_view::iterator_)
`friend constexpr iterator operator+(difference_type n, iterator i)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[21](#21)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3438)
*Effects*: Equivalent to: return i + n;
[🔗](#lib:operator-,iota_view::iterator)
`friend constexpr iterator operator-(iterator i, difference_type n)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[22](#22)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3450)
*Effects*: Equivalent to:i -= n;return i;
[🔗](#lib:operator-,iota_view::iterator_)
`friend constexpr difference_type operator-(const iterator& x, const iterator& y)
requires [advanceable](range.iota.view#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>;
`
[23](#23)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3466)
*Effects*: Equivalent to:using D = difference_type;if constexpr (*is-integer-like*<W>) {if constexpr (*is-signed-integer-like*<W>)return D(D(x.*value_*) - D(y.*value_*)); elsereturn (y.*value_* > x.*value_*)? D(-D(y.*value_* - x.*value_*)): D(x.*value_* - y.*value_*);} else {return x.*value_* - y.*value_*;}

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[range.iota.overview]
# 25 Ranges library [[ranges]](./#ranges)
## 25.6 Range factories [[range.factories]](range.factories#range.iota.overview)
### 25.6.4 Iota view [[range.iota]](range.iota#overview)
#### 25.6.4.1 Overview [range.iota.overview]
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2778)
iota_view generates a
sequence of elements by repeatedly incrementing an initial value[.](#1.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2782)
The name views​::​iota denotes a
customization point object ([[customization.point.object]](customization.point.object "16.3.3.3.5 Customization Point Object types"))[.](#2.sentence-1)
Given subexpressions E and F, the expressionsviews​::​iota(E) and views​::​iota(E, F) are expression-equivalent toiota_view<decay_t<decltype((E))>>(E) and iota_view(E, F),
respectively[.](#2.sentence-2)
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2792)
[*Example [1](#example-1)*: for (int i : views::iota(1, 10)) cout << i << ' '; // prints 1 2 3 4 5 6 7 8 9 — *end example*]
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2800)
The name views​::​indices denotes a
customization point object ([[customization.point.object]](customization.point.object "16.3.3.3.5 Customization Point Object types"))[.](#4.sentence-1)
Given subexpression E,
let T be remove_cvref_t<decltype((E))>[.](#4.sentence-2)
views​::​indices(E) is expression-equivalent toviews​::​iota(T(0), E) if *is-integer-like*<T> is true,
and ill-formed otherwise[.](#4.sentence-3)

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[range.iota.sentinel]
# 25 Ranges library [[ranges]](./#ranges)
## 25.6 Range factories [[range.factories]](range.factories#range.iota.sentinel)
### 25.6.4 Iota view [[range.iota]](range.iota#sentinel)
#### 25.6.4.4 Class iota_view​::​*sentinel* [range.iota.sentinel]
[🔗](#lib:iota_view::sentinel)
namespace std::ranges {template<[weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") W, [semiregular](concepts.object#concept:semiregular "18.6 Object concepts [concepts.object]") Bound>requires [*weakly-equality-comparable-with*](concept.equalitycomparable#concept:weakly-equality-comparable-with "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<W, Bound> && [copyable](concepts.object#concept:copyable "18.6 Object concepts [concepts.object]")<W>struct iota_view<W, Bound>::*sentinel* {private: Bound *bound_* = Bound(); // *exposition only*public:*sentinel*() = default; constexpr explicit *sentinel*(Bound bound); friend constexpr bool operator==(const *iterator*& x, const *sentinel*& y); friend constexpr iter_difference_t<W> operator-(const *iterator*& x, const *sentinel*& y)requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<Bound, W>; friend constexpr iter_difference_t<W> operator-(const *sentinel*& 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]")<Bound, W>; };}
[🔗](#lib:iota_view::sentinel,constructor)
`constexpr explicit sentinel(Bound bound);
`
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3515)
*Effects*: Initializes *bound_* with bound[.](#1.sentence-1)
[🔗](#lib:operator==,iota_view::sentinel)
`friend constexpr bool operator==(const iterator& x, const sentinel& y);
`
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3526)
*Effects*: Equivalent to: return x.*value_* == y.*bound_*;
[🔗](#lib:operator-,iota_view::sentinel)
`friend constexpr iter_difference_t<W> operator-(const iterator& x, const sentinel& y)
requires [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<Bound, W>;
`
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3538)
*Effects*: Equivalent to: return x.*value_* - y.*bound_*;
[🔗](#lib:operator-,iota_view::sentinel_)
`friend constexpr iter_difference_t<W> operator-(const sentinel& 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]")<Bound, W>;
`
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3550)
*Effects*: Equivalent to: return -(y - x);

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[range.iota.view]
# 25 Ranges library [[ranges]](./#ranges)
## 25.6 Range factories [[range.factories]](range.factories#range.iota.view)
### 25.6.4 Iota view [[range.iota]](range.iota#view)
#### 25.6.4.2 Class template iota_view [range.iota.view]
[🔗](#lib:iota_view)
namespace std::ranges {template<class I>concept [*decrementable*](#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]") = *see below*; // *exposition only*template<class I>concept [*advanceable*](#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]") = *see below*; // *exposition only*template<[weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") W, [semiregular](concepts.object#concept:semiregular "18.6 Object concepts [concepts.object]") Bound = unreachable_sentinel_t>requires [*weakly-equality-comparable-with*](concept.equalitycomparable#concept:weakly-equality-comparable-with "18.5.4 Concept equality_­comparable [concept.equalitycomparable]")<W, Bound> && [copyable](concepts.object#concept:copyable "18.6 Object concepts [concepts.object]")<W>class iota_view : public view_interface<iota_view<W, Bound>> {private:// [[range.iota.iterator]](range.iota.iterator "25.6.4.3 Class iota_­view​::​iterator"), class iota_view​::​*iterator*struct *iterator*; // *exposition only*// [[range.iota.sentinel]](range.iota.sentinel "25.6.4.4 Class iota_­view​::​sentinel"), class iota_view​::​*sentinel*struct *sentinel*; // *exposition only* W *value_* = W(); // *exposition only* Bound *bound_* = Bound(); // *exposition only*public: iota_view() requires [default_initializable](concept.default.init#concept:default_initializable "18.4.12 Concept default_­initializable [concept.default.init]")<W> = default; constexpr explicit iota_view(W value); constexpr explicit iota_view(type_identity_t<W> value, type_identity_t<Bound> bound); constexpr explicit iota_view(*iterator* first, *see below* last); constexpr *iterator* begin() const; constexpr auto end() const; constexpr *iterator* end() const requires [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<W, Bound>; constexpr bool empty() const; constexpr auto size() const requires *see below*; }; template<class W, class Bound>requires (!*is-integer-like*<W> || !*is-integer-like*<Bound> ||(*is-signed-integer-like*<W> == *is-signed-integer-like*<Bound>)) iota_view(W, Bound) -> iota_view<W, Bound>;}
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2856)
Let *IOTA-DIFF-T*(W) be defined as follows:
- [(1.1)](#1.1)
If W is not an integral type, or
if it is an integral type and sizeof(iter_difference_t<W>) is greater than sizeof(W),
then *IOTA-DIFF-T*(W) denotes iter_difference_t<W>[.](#1.1.sentence-1)
- [(1.2)](#1.2)
Otherwise, *IOTA-DIFF-T*(W) is a signed integer type of width greater than the width of W if such a type exists[.](#1.2.sentence-1)
- [(1.3)](#1.3)
Otherwise, *IOTA-DIFF-T*(W) is an unspecified signed-integer-like type ([[iterator.concept.winc]](iterator.concept.winc "24.3.4.4 Concept weakly_­incrementable"))
of width not less than the width of W[.](#1.3.sentence-1)
[*Note [1](#note-1)*:
It is unspecified
whether this type satisfies [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]")[.](#1.3.sentence-2)
— *end note*]
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2878)
The exposition-only [*decrementable*](#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]") concept is equivalent to:
[🔗](#concept:decrementable)
`template<class I>
concept [decrementable](#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]") = // exposition only
[incrementable](iterator.concept.inc#concept:incrementable "24.3.4.5 Concept incrementable [iterator.concept.inc]")<I> && requires(I i) {
{ --i } -> [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<I&>;
{ i-- } -> [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<I>;
};
`
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2890)
When an object is in the domain of both pre- and post-decrement,
the object is said to be [*decrementable*](#def:decrementable)[.](#3.sentence-1)
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2894)
Let a and b be equal objects of type I[.](#4.sentence-1)
I models [*decrementable*](#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]") only if
- [(4.1)](#4.1)
If a and b are decrementable,
then the following are all true:
* [(4.1.1)](#4.1.1)
addressof(--a) == addressof(a)
* [(4.1.2)](#4.1.2)
bool(a-- == b)
* [(4.1.3)](#4.1.3)
bool(((void)a--, a) == --b)
* [(4.1.4)](#4.1.4)
bool(++(--a) == b)[.](#4.1.sentence-1)
- [(4.2)](#4.2)
If a and b are incrementable,
then bool(--(++a) == b)[.](#4.2.sentence-1)
[5](#5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2911)
The exposition-only [*advanceable*](#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]") concept is equivalent to:
[🔗](#concept:advanceable)
`template<class I>
concept [advanceable](#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]") = // exposition only
[decrementable](#concept:decrementable "25.6.4.2 Class template iota_­view [range.iota.view]")<I> && [totally_ordered](concept.totallyordered#concept:totally_ordered "18.5.5 Concept totally_­ordered [concept.totallyordered]")<I> &&
requires(I i, const I j, const IOTA-DIFF-T(I) n) {
{ i += n } -> [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<I&>;
{ i -= n } -> [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<I&>;
I(j + n);
I(n + j);
I(j - n);
{ j - j } -> [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<IOTA-DIFF-T(I)>;
};
`
Let D be *IOTA-DIFF-T*(I)[.](#sentence-1)
Let a and b be objects of type I such thatb is reachable from a after n applications of ++a,
for some value n of type D[.](#sentence-2)
I models [*advanceable*](#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]") only if
- (a += n) is equal to b[.](#sentence-1)
- addressof(a += n) is equal to addressof(a)[.](#sentence-1)
- I(a + n) is equal to (a += n)[.](#sentence-1)
- For any two positive values x and y of type D,
if I(a + D(x + y)) is well-defined, then I(a + D(x + y)) is equal to I(I(a + x) + y)[.](#sentence-1)
- I(a + D(0)) is equal to a[.](#sentence-1)
- If I(a + D(n - 1)) is well-defined, then I(a + n) is equal to [](I c) { return ++c; }(I(a + D(n - 1)))[.](#sentence-1)
- (b += -n) is equal to a[.](#sentence-1)
- (b -= n) is equal to a[.](#sentence-1)
- addressof(b -= n) is equal to addressof(b)[.](#sentence-1)
- I(b - n) is equal to (b -= n)[.](#sentence-1)
- D(b - a) is equal to n[.](#sentence-1)
- D(a - b) is equal to D(-n)[.](#sentence-1)
- bool(a <= b) is true[.](#sentence-1)
[🔗](#lib:iota_view,constructor)
`constexpr explicit iota_view(W value);
`
[6](#6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2959)
*Preconditions*: Bound denotes unreachable_sentinel_t orBound() is reachable from value[.](#6.sentence-1)
When W and Bound model [totally_ordered_with](concept.totallyordered#concept:totally_ordered_with "18.5.5 Concept totally_­ordered [concept.totallyordered]"),
then bool(value <= Bound()) is true[.](#6.sentence-2)
[7](#7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2966)
*Effects*: Initializes *value_* with value[.](#7.sentence-1)
[🔗](#lib:iota_view,constructor_)
`constexpr explicit iota_view(type_identity_t<W> value, type_identity_t<Bound> bound);
`
[8](#8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2977)
*Preconditions*: Bound denotes unreachable_sentinel_t orbound is reachable from value[.](#8.sentence-1)
When W and Bound model [totally_ordered_with](concept.totallyordered#concept:totally_ordered_with "18.5.5 Concept totally_­ordered [concept.totallyordered]"),
then bool(value <= bound) is true[.](#8.sentence-2)
[9](#9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2984)
*Effects*: Initializes *value_* with value and*bound_* with bound[.](#9.sentence-1)
[🔗](#lib:iota_view,constructor__)
`constexpr explicit iota_view(iterator first, see below last);
`
[10](#10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L2996)
*Effects*: Equivalent to:
- [(10.1)](#10.1)
If [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<W, Bound> is true,iota_view(first.*value_*, last.*value_*)[.](#10.1.sentence-1)
- [(10.2)](#10.2)
Otherwise, if Bound denotes unreachable_sentinel_t,iota_view(first.*value_*, last)[.](#10.2.sentence-1)
- [(10.3)](#10.3)
Otherwise, iota_view(first.*value_*, last.*bound_*)[.](#10.3.sentence-1)
[11](#11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3010)
*Remarks*: The type of last is:
- [(11.1)](#11.1)
If [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<W, Bound> is true, *iterator*[.](#11.1.sentence-1)
- [(11.2)](#11.2)
Otherwise, if Bound denotes unreachable_sentinel_t,Bound[.](#11.2.sentence-1)
- [(11.3)](#11.3)
Otherwise, *sentinel*[.](#11.3.sentence-1)
[🔗](#lib:begin,iota_view)
`constexpr iterator begin() const;
`
[12](#12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3030)
*Effects*: Equivalent to: return *iterator*{*value_*};
[🔗](#lib:end,iota_view)
`constexpr auto end() const;
`
[13](#13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3041)
*Effects*: Equivalent to:if constexpr ([same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<Bound, unreachable_sentinel_t>)return unreachable_sentinel;elsereturn *sentinel*{*bound_*};
[🔗](#lib:end,iota_view_)
`constexpr iterator end() const requires [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<W, Bound>;
`
[14](#14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3058)
*Effects*: Equivalent to: return *iterator*{*bound_*};
[🔗](#lib:empty,iota_view)
`constexpr bool empty() const;
`
[15](#15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3069)
*Effects*: Equivalent to: return *value_* == *bound_*;
[🔗](#lib:size,iota_view)
`constexpr auto size() const requires see below;
`
[16](#16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3080)
*Effects*: Equivalent to:if constexpr (*is-integer-like*<W> && *is-integer-like*<Bound>)return (*value_* < 0)? ((*bound_* < 0)? *to-unsigned-like*(-*value_*) - *to-unsigned-like*(-*bound_*): *to-unsigned-like*(*bound_*) + *to-unsigned-like*(-*value_*)): *to-unsigned-like*(*bound_*) - *to-unsigned-like*(*value_*);elsereturn *to-unsigned-like*(*bound_* - *value_*);
[17](#17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L3094)
*Remarks*: The expression in the [*requires-clause*](temp.pre#nt:requires-clause "13.1 Preamble [temp.pre]") is equivalent to:([same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<W, Bound> && [*advanceable*](#concept:advanceable "25.6.4.2 Class template iota_­view [range.iota.view]")<W>) || (*is-integer-like*<W> && *is-integer-like*<Bound>) ||[sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<Bound, W>