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cppdraft_translate/cppdraft/range/concat/iterator.md
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[range.concat.iterator]
# 25 Ranges library [[ranges]](./#ranges)
## 25.7 Range adaptors [[range.adaptors]](range.adaptors#range.concat.iterator)
### 25.7.18 Concat view [[range.concat]](range.concat#iterator)
#### 25.7.18.3 Class concat_view​::​*iterator* [range.concat.iterator]
[🔗](#lib:iterator,concat_view)
namespace std::ranges {template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]")... Views>requires ([view](range.view#concept:view "25.4.5 Views [range.view]")<Views> && ...) && (sizeof...(Views) > 0) &&[*concatable*](range.concat.view#concept:concatable "25.7.18.2 Class template concat_­view [range.concat.view]")<Views...>template<bool Const>class concat_view<Views...>::*iterator* {public:using iterator_category = *see below*; // not always presentusing iterator_concept = *see below*; using value_type = *concat-value-t*<*maybe-const*<Const, Views>...>; using difference_type = common_type_t<range_difference_t<*maybe-const*<Const, Views>>...>; private:using *base-iter* = // *exposition only* variant<iterator_t<*maybe-const*<Const, Views>>...>; *maybe-const*<Const, concat_view>* *parent_* = nullptr; // *exposition only**base-iter* *it_*; // *exposition only*template<size_t N>constexpr void *satisfy*(); // *exposition only*template<size_t N>constexpr void *prev*(); // *exposition only*template<size_t N>constexpr void *advance-fwd*(difference_type offset, // *exposition only* difference_type steps); template<size_t N>constexpr void *advance-bwd*(difference_type offset, // *exposition only* difference_type steps); template<class... Args>constexpr explicit *iterator*(*maybe-const*<Const, concat_view>* parent, // *exposition only* Args&&... args)requires [constructible_from](concept.constructible#concept:constructible_from "18.4.11 Concept constructible_­from [concept.constructible]")<*base-iter*, Args&&...>; public:*iterator*() = default; constexpr *iterator*(*iterator*<!Const> i)requires Const && ([convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<iterator_t<Views>, iterator_t<const Views>> && ...); constexpr decltype(auto) operator*() const; constexpr *iterator*& operator++(); constexpr void operator++(int); constexpr *iterator* operator++(int)requires [*all-forward*](range.adaptor.helpers#concept:all-forward "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>; constexpr *iterator*& operator--()requires [*concat-is-bidirectional*](range.concat.view#concept:concat-is-bidirectional "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; constexpr *iterator* operator--(int)requires [*concat-is-bidirectional*](range.concat.view#concept:concat-is-bidirectional "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; constexpr *iterator*& operator+=(difference_type n)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; constexpr *iterator*& operator-=(difference_type n)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; constexpr decltype(auto) operator[](difference_type n) constrequires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; 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<*maybe-const*<Const, Views>>> && ...); friend constexpr bool operator==(const *iterator*& it, default_sentinel_t); friend constexpr bool operator<(const *iterator*& x, const *iterator*& y)requires [*all-random-access*](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>; friend constexpr bool operator>(const *iterator*& x, const *iterator*& y)requires [*all-random-access*](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>; friend constexpr bool operator<=(const *iterator*& x, const *iterator*& y)requires [*all-random-access*](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>; friend constexpr bool operator>=(const *iterator*& x, const *iterator*& y)requires [*all-random-access*](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>; friend constexpr auto operator<=>(const *iterator*& x, const *iterator*& y)requires ([*all-random-access*](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...> &&([three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<iterator_t<*maybe-const*<Const, Views>>> && ...)); friend constexpr *iterator* operator+(const *iterator*& it, difference_type n)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; friend constexpr *iterator* operator+(difference_type n, const *iterator*& it)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; friend constexpr *iterator* operator-(const *iterator*& it, difference_type n)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; friend constexpr difference_type operator-(const *iterator*& x, const *iterator*& y)requires [*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>; friend constexpr difference_type operator-(const *iterator*& x, default_sentinel_t)requires *see below*; friend constexpr difference_type operator-(default_sentinel_t, const *iterator*& x)requires *see below*; friend constexpr decltype(auto) iter_move(const *iterator*& it) noexcept(*see below*); friend constexpr void iter_swap(const *iterator*& x, const *iterator*& y) noexcept(*see below*)requires *see below*; };}
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9035)
*iterator*​::​iterator_concept is defined as follows:
- [(1.1)](#1.1)
If[*concat-is-random-access*](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...> is modeled,
then iterator_concept denotes random_access_iterator_tag[.](#1.1.sentence-1)
- [(1.2)](#1.2)
Otherwise, if[*concat-is-bidirectional*](range.concat.view#concept:concat-is-bidirectional "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...> is modeled,
then iterator_concept denotes bidirectional_iterator_tag[.](#1.2.sentence-1)
- [(1.3)](#1.3)
Otherwise, if[*all-forward*](range.adaptor.helpers#concept:all-forward "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...> is modeled,
then iterator_concept denotes forward_iterator_tag[.](#1.3.sentence-1)
- [(1.4)](#1.4)
Otherwise, iterator_concept denotes input_iterator_tag[.](#1.4.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9054)
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[*all-forward*](range.adaptor.helpers#concept:all-forward "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...> is modeled[.](#2.sentence-1)
In that case,*iterator*​::​iterator_category is defined as follows:
- [(2.1)](#2.1)
Ifis_reference_v<*concat-reference-t*<*maybe-const*<Const, Views>...>> is false,
then iterator_category denotes input_iterator_tag[.](#2.1.sentence-1)
- [(2.2)](#2.2)
Otherwise,
let Cs denote the pack of typesiterator_traits<iterator_t<*maybe-const*<Const, Views>>>​::​iterator_category...[.](#2.2.sentence-1)
* [(2.2.1)](#2.2.1)
If([derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<Cs, random_access_iterator_tag> && ...) && *concat-is-random-access*<Const, Views...> is true,iterator_category denotes random_access_iterator_tag[.](#2.2.1.sentence-1)
* [(2.2.2)](#2.2.2)
Otherwise, if([derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<Cs, bidirectional_iterator_tag> && ...) && *concat-is-bidirectional*<Const, Views...> is true,iterator_category denotes bidirectional_iterator_tag[.](#2.2.2.sentence-1)
* [(2.2.3)](#2.2.3)
Otherwise, if([derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<Cs, forward_iterator_tag> && ...) is true,iterator_category denotes forward_iterator_tag[.](#2.2.3.sentence-1)
* [(2.2.4)](#2.2.4)
Otherwise, iterator_category denotes input_iterator_tag[.](#2.2.4.sentence-1)
[🔗](#lib:satisfy,concat_view::iterator)
`template<size_t N>
constexpr void satisfy();
`
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9100)
*Effects*: Equivalent to:if constexpr (N < (sizeof...(Views) - 1)) {if (std::get<N>(*it_*) == ranges::end(std::get<N>(*parent_*->*views_*))) {*it_*.template emplace<N + 1>(ranges::begin(std::get<N + 1>(*parent_*->*views_*))); *satisfy*<N + 1>(); }}
[🔗](#lib:prev,concat_view::iterator)
`template<size_t N>
constexpr void prev();
`
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9120)
*Effects*: Equivalent to:if constexpr (N == 0) {--std::get<0>(*it_*);} else {if (std::get<N>(*it_*) == ranges::begin(std::get<N>(*parent_*->*views_*))) {*it_*.template emplace<N - 1>(ranges::end(std::get<N - 1>(*parent_*->*views_*))); *prev*<N - 1>(); } else {--std::get<N>(*it_*); }}
[🔗](#lib:advance-fwd,concat_view::iterator)
`template<size_t N>
constexpr void advance-fwd(difference_type offset, difference_type steps);
`
[5](#5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9144)
*Effects*: Equivalent to:using underlying_diff_type = iter_difference_t<variant_alternative_t<N, *base-iter*>>;if constexpr (N == sizeof...(Views) - 1) { std::get<N>(*it_*) += static_cast<underlying_diff_type>(steps);} else {auto n_size = ranges::distance(std::get<N>(*parent_*->*views_*)); if (offset + steps < n_size) { std::get<N>(*it_*) += static_cast<underlying_diff_type>(steps); } else {*it_*.template emplace<N + 1>(ranges::begin(std::get<N + 1>(*parent_*->*views_*))); *advance-fwd*<N + 1>(0, offset + steps - n_size); }}
[🔗](#lib:advance-bwd,concat_view::iterator)
`template<size_t N>
constexpr void advance-bwd(difference_type offset, difference_type steps);
`
[6](#6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9170)
*Effects*: Equivalent to:using underlying_diff_type = iter_difference_t<variant_alternative_t<N, *base-iter*>>;if constexpr (N == 0) { std::get<N>(*it_*) -= static_cast<underlying_diff_type>(steps);} else {if (offset >= steps) { std::get<N>(*it_*) -= static_cast<underlying_diff_type>(steps); } else {auto prev_size = ranges::distance(std::get<N - 1>(*parent_*->*views_*)); *it_*.template emplace<N - 1>(ranges::end(std::get<N - 1>(*parent_*->*views_*))); *advance-bwd*<N - 1>(prev_size, steps - offset); }}
[🔗](#lib:concat_view::iterator,constructor)
`template<class... Args>
constexpr explicit iterator(maybe-const<Const, concat_view>* parent,
Args&&... args)
requires [constructible_from](concept.constructible#concept:constructible_from "18.4.11 Concept constructible_­from [concept.constructible]")<base-iter, Args&&...>;
`
[7](#7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9198)
*Effects*: Initializes *parent_* with parent, and
initializes *it_* with std​::​forward<Args>(args)...[.](#7.sentence-1)
[🔗](#lib:concat_view::iterator,constructor_)
`constexpr iterator(iterator<!Const> it)
requires Const &&
([convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<iterator_t<Views>, iterator_t<const Views>> && ...);
`
[8](#8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9212)
*Preconditions*: it.*it_*.valueless_by_exception() is false[.](#8.sentence-1)
[9](#9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9216)
*Effects*: Initializes *parent_* with it.*parent_*, and
let i be it.*it_*.index(),
initializes *it_* with*base-iter*(in_place_index<i>, std​::​get<i>(std​::​move(it.*it_*)))[.](#9.sentence-1)
[🔗](#lib:operator*,concat_view::iterator)
`constexpr decltype(auto) operator*() const;
`
[10](#10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9230)
*Preconditions*: *it_*.valueless_by_exception() is false[.](#10.sentence-1)
[11](#11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9234)
*Effects*: Equivalent to:using reference = *concat-reference-t*<*maybe-const*<Const, Views>...>;return std::visit([](auto&& it) -> reference { return *it; }, *it_*);
[🔗](#lib:operator++,concat_view::iterator)
`constexpr iterator& operator++();
`
[12](#12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9250)
*Preconditions*: *it_*.valueless_by_exception() is false[.](#12.sentence-1)
[13](#13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9254)
*Effects*: Let i be *it_*.index()[.](#13.sentence-1)
Equivalent to:++std::get<i>(*it_*);*satisfy*<i>();return *this;
[🔗](#lib:operator++,concat_view::iterator_)
`constexpr void operator++(int);
`
[14](#14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9271)
*Effects*: Equivalent to:++*this;
[🔗](#lib:operator++,concat_view::iterator__)
`constexpr iterator operator++(int)
requires [all-forward](range.adaptor.helpers#concept:all-forward "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>;
`
[15](#15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9286)
*Effects*: Equivalent to:auto tmp = *this;++*this;return tmp;
[🔗](#lib:operator--,concat_view::iterator)
`constexpr iterator& operator--()
requires [concat-is-bidirectional](range.concat.view#concept:concat-is-bidirectional "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[16](#16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9303)
*Preconditions*: *it_*.valueless_by_exception() is false[.](#16.sentence-1)
[17](#17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9307)
*Effects*: Let i be *it_*.index()[.](#17.sentence-1)
Equivalent to:*prev*<i>();return *this;
[🔗](#lib:operator--,concat_view::iterator_)
`constexpr iterator operator--(int)
requires [concat-is-bidirectional](range.concat.view#concept:concat-is-bidirectional "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[18](#18)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9324)
*Effects*: Equivalent to:auto tmp = *this;--*this;return tmp;
[🔗](#lib:operator+=,concat_view::iterator)
`constexpr iterator& operator+=(difference_type n)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[19](#19)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9341)
*Preconditions*: *it_*.valueless_by_exception() is false[.](#19.sentence-1)
[20](#20)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9345)
*Effects*: Let i be *it_*.index()[.](#20.sentence-1)
Equivalent to:if (n > 0) {*advance-fwd*<i>(std::get<i>(*it_*) - ranges::begin(std::get<i>(*parent_*->*views_*)), n);} else if (n < 0) {*advance-bwd*<i>(std::get<i>(*it_*) - ranges::begin(std::get<i>(*parent_*->*views_*)), -n);}return *this;
[🔗](#lib:operator-=,concat_view::iterator)
`constexpr iterator& operator-=(difference_type n)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[21](#21)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9366)
*Effects*: Equivalent to:*this += -n;return *this;
[🔗](#lib:operator%5b%5d,concat_view::iterator)
`constexpr decltype(auto) operator[](difference_type n) const
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[22](#22)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9382)
*Effects*: Equivalent to:return *((*this) + n);
[🔗](#lib:operator==,concat_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]")<iterator_t<maybe-const<Const, Views>>> && ...);
`
[23](#23)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9397)
*Preconditions*: x.*it_*.valueless_by_exception() andy.*it_*.valueless_by_exception() are each false[.](#23.sentence-1)
[24](#24)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9402)
*Effects*: Equivalent to:return x.*it_* == y.*it_*;
[🔗](#lib:operator==,concat_view::iterator_)
`friend constexpr bool operator==(const iterator& it, default_sentinel_t);
`
[25](#25)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9416)
*Preconditions*: it.*it_*.valueless_by_exception() is false[.](#25.sentence-1)
[26](#26)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9420)
*Effects*: Equivalent to:constexpr auto last_idx = sizeof...(Views) - 1;return it.*it_*.index() == last_idx && std::get<last_idx>(it.*it_*) == ranges::end(std::get<last_idx>(it.*parent_*->*views_*));
[🔗](#lib:operator%3c,concat_view::iterator)
`friend constexpr bool operator<(const iterator& x, const iterator& y)
requires [all-random-access](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>;
friend constexpr bool operator>(const iterator& x, const iterator& y)
requires [all-random-access](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>;
friend constexpr bool operator<=(const iterator& x, const iterator& y)
requires [all-random-access](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>;
friend constexpr bool operator>=(const iterator& x, const iterator& y)
requires [all-random-access](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...>;
friend constexpr auto operator<=>(const iterator& x, const iterator& y)
requires ([all-random-access](range.adaptor.helpers#concept:all-random-access "25.7.5 Range adaptor helpers [range.adaptor.helpers]")<Const, Views...> &&
([three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<iterator_t<maybe-const<Const, Views>>> && ...));
`
[27](#27)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9446)
*Preconditions*: x.*it_*.valueless_by_exception() andy.*it_*.valueless_by_exception() are each false[.](#27.sentence-1)
[28](#28)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9451)
Let op be the operator[.](#28.sentence-1)
[29](#29)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9454)
*Effects*: Equivalent to:return x.*it_* op y.*it_*;
[🔗](#lib:operator+,concat_view::iterator)
`friend constexpr iterator operator+(const iterator& it, difference_type n)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[30](#30)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9469)
*Effects*: Equivalent to:auto temp = it;
temp += n;return temp;
[🔗](#lib:operator+,concat_view::iterator_)
`friend constexpr iterator operator+(difference_type n, const iterator& it)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[31](#31)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9486)
*Effects*: Equivalent to:return it + n;
[🔗](#lib:operator-,concat_view::iterator)
`friend constexpr iterator operator-(const iterator& it, difference_type n)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[32](#32)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9501)
*Effects*: Equivalent to:auto temp = it;
temp -= n;return temp;
[🔗](#lib:operator-,concat_view::iterator_)
`friend constexpr difference_type operator-(const iterator& x, const iterator& y)
requires [concat-is-random-access](range.concat.view#concept:concat-is-random-access "25.7.18.2 Class template concat_­view [range.concat.view]")<Const, Views...>;
`
[33](#33)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9518)
*Preconditions*: x.*it_*.valueless_by_exception() andy.*it_*.valueless_by_exception() are each false[.](#33.sentence-1)
[34](#34)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9523)
*Effects*: Letix denote x.*it_*.index() andiy denote y.*it_*.index()[.](#34.sentence-1)
- [(34.1)](#34.1)
If ix > iy, letdy beranges​::​distance(std​::​get<iy>(y.*it_*), ranges​::​end(std​::​get<iy>(y.*parent_*->*views_*))),dx beranges​::​distance(ranges​::​begin(std​::​get<ix>(x.*parent_*->*views_*)), std​::​get<ix>(x.*it_*)). Let s denote the sum of the sizes of all the rangesstd​::​get<i>(x.*parent_*->*views_*) for every integer i in the range
[iy + 1, ix)
if there is any, and0 otherwise,
of type difference_type,
equivalent to:return dy + s + dx;
- [(34.2)](#34.2)
otherwise, if ix < iy is true,
equivalent to:return -(y - x);
- [(34.3)](#34.3)
otherwise, equivalent to:return std::get<ix>(x.*it_*) - std::get<iy>(y.*it_*);
[🔗](#lib:operator-,concat_view::iterator__)
`friend constexpr difference_type operator-(const iterator& x, default_sentinel_t)
requires see below;
`
[35](#35)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9571)
*Preconditions*: x.*it_*.valueless_by_exception() is false[.](#35.sentence-1)
[36](#36)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9575)
*Effects*: Letix denote x.*it_*.index(),dx beranges​::​distance(std​::​get<ix>(x.*it_*), ranges​::​end(std​::​get<ix>(x.*parent_*->*views_*)))[.](#36.sentence-1)
Let s denote the sum of the sizes of all the rangesstd​::​get<i>(x.*parent_*->*views_*) for every integer i in the range
[ix + 1, sizeof...(Views))
if there is any, and0 otherwise,
of type difference_type,
equivalent to:return -(dx + s);
[37](#37)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9594)
*Remarks*: Let Fs be the pack that consists of all elements of Views except the first element,
the expression in the [*requires-clause*](temp.pre#nt:requires-clause "13.1 Preamble [temp.pre]") is equivalent to:([sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<*maybe-const*<Const, Views>>,
iterator_t<*maybe-const*<Const, Views>>> && ...) &&([sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<*maybe-const*<Const, Fs>> && ...)
[🔗](#lib:operator-,concat_view::iterator___)
`friend constexpr difference_type operator-(default_sentinel_t, const iterator& x)
requires see below;
`
[38](#38)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9614)
*Effects*: Equivalent to:return -(x - default_sentinel);
[39](#39)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9621)
*Remarks*: Let Fs be the pack that consists of all elements of Views except the first element,
the expression in the [*requires-clause*](temp.pre#nt:requires-clause "13.1 Preamble [temp.pre]") is equivalent to:([sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<sentinel_t<*maybe-const*<Const, Views>>,
iterator_t<*maybe-const*<Const, Views>>> && ...) &&([sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]")<*maybe-const*<Const, Fs>> && ...)
[🔗](#lib:iter_move,concat_view::iterator)
`friend constexpr decltype(auto) iter_move(const iterator& it) noexcept(see below);
`
[40](#40)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9639)
*Preconditions*: it.*it_*.valueless_by_exception() is false[.](#40.sentence-1)
[41](#41)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9643)
*Effects*: Equivalent to:return std::visit([](const auto& i)-> *concat-rvalue-reference-t*<*maybe-const*<Const, Views>...> {return ranges::iter_move(i); },
it.*it_*);
[42](#42)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9654)
*Remarks*: The exception specification is equivalent to:((is_nothrow_invocable_v<decltype(ranges::iter_move), const iterator_t<*maybe-const*<Const, Views>>&> && is_nothrow_convertible_v<range_rvalue_reference_t<*maybe-const*<Const, Views>>, *concat-rvalue-reference-t*<*maybe-const*<Const, Views>...>>) &&...)
[🔗](#lib:iter_swap,concat_view::iterator)
`friend constexpr void iter_swap(const iterator& x, const iterator& y) noexcept(see below)
requires see below;
`
[43](#43)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9673)
*Preconditions*: x.*it_*.valueless_by_exception() andy.*it_*.valueless_by_exception() are each false[.](#43.sentence-1)
[44](#44)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9678)
*Effects*: Equivalent to:std::visit([&](const auto& it1, const auto& it2) {if constexpr (is_same_v<decltype(it1), decltype(it2)>) { ranges::iter_swap(it1, it2); } else { ranges::swap(*x, *y); }},
x.*it_*, y.*it_*);
[45](#45)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/ranges.tex#L9692)
*Remarks*: The exception specification is equivalent to(noexcept(ranges::swap(*x, *y)) && ... && noexcept(ranges::iter_swap(its, its))) where its is a pack of lvalues of typeconst iterator_t<*maybe-const*<Const, Views>> respectively[.](#45.sentence-1)
The expression in the [*requires-clause*](temp.pre#nt:requires-clause "13.1 Preamble [temp.pre]") is equivalent to[swappable_with](concept.swappable#concept:swappable_with "18.4.9 Concept swappable [concept.swappable]")<iter_reference_t<*iterator*>, iter_reference_t<*iterator*>> &&(... && [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<iterator_t<*maybe-const*<Const, Views>>>)
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