26 Ranges library [ranges]

26.7 Range adaptors [range.adaptors]

26.7.24 Zip view [range.zip]

26.7.24.1 Overview [range.zip.overview]

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zip_view takes any number of views and produces a view of tuples of references to the corresponding elements of the constituent views.
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The name views​::​zip denotes a customization point object ([customization.point.object]).
Given a pack of subexpressions Es..., the expression views​::​zip(Es...) is expression-equivalent to
  • (2.1)
    auto(views​::​empty<tuple<>>) if Es is an empty pack,
  • (2.2)
    otherwise, zip_view<views​::​all_t<decltype((Es))>...>(Es...).
[Example 1: vector v = {1, 2}; list l = {'a', 'b', 'c'}; auto z = views::zip(v, l); range_reference_t<decltype(z)> f = z.front(); // f is a tuple<int&, char&> // that refers to the first element of v and l for (auto&& [x, y] : z) { cout << '(' << x << ", " << y << ") "; // prints (1, a) (2, b) } — end example]

26.7.24.2 Class template zip_view [range.zip.view]

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namespace std::ranges { template<class... Rs> concept zip-is-common = // exposition only (sizeof...(Rs) == 1 && (common_range<Rs> && ...)) || (!(bidirectional_range<Rs> && ...) && (common_range<Rs> && ...)) || ((random_access_range<Rs> && ...) && (sized_range<Rs> && ...)); template<input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) class zip_view : public view_interface<zip_view<Views...>> { tuple<Views...> views_; // exposition only // [range.zip.iterator], class template zip_view​::​iterator template<bool> class iterator; // exposition only // [range.zip.sentinel], class template zip_view​::​sentinel template<bool> class sentinel; // exposition only public: zip_view() = default; constexpr explicit zip_view(Views... views); constexpr auto begin() requires (!(simple-view<Views> && ...)) { return iterator<false>(tuple-transform(ranges::begin, views_)); } constexpr auto begin() const requires (range<const Views> && ...) { return iterator<true>(tuple-transform(ranges::begin, views_)); } constexpr auto end() requires (!(simple-view<Views> && ...)) { if constexpr (!zip-is-common<Views...>) { return sentinel<false>(tuple-transform(ranges::end, views_)); } else if constexpr ((random_access_range<Views> && ...)) { return begin() + iter_difference_t<iterator<false>>(size()); } else { return iterator<false>(tuple-transform(ranges::end, views_)); } } constexpr auto end() const requires (range<const Views> && ...) { if constexpr (!zip-is-common<const Views...>) { return sentinel<true>(tuple-transform(ranges::end, views_)); } else if constexpr ((random_access_range<const Views> && ...)) { return begin() + iter_difference_t<iterator<true>>(size()); } else { return iterator<true>(tuple-transform(ranges::end, views_)); } } constexpr auto size() requires (sized_range<Views> && ...); constexpr auto size() const requires (sized_range<const Views> && ...); }; template<class... Rs> zip_view(Rs&&...) -> zip_view<views::all_t<Rs>...>; }
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Two zip_view objects have the same underlying sequence if and only if the corresponding elements of views_ are equal ([concepts.equality]) and have the same underlying sequence.
[Note 1: 
In particular, comparison of iterators obtained from zip_view objects that do not have the same underlying sequence is not required to produce meaningful results ([iterator.concept.forward]).
— end note]
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constexpr explicit zip_view(Views... views);
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Effects: Initializes views_ with std​::​move(views)....
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constexpr auto size() requires (sized_range<Views> && ...); constexpr auto size() const requires (sized_range<const Views> && ...);
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Effects: Equivalent to: return apply([](auto... sizes) { using CT = make-unsigned-like-t<common_type_t<decltype(sizes)...>>; return ranges::min({CT(sizes)...}); }, tuple-transform(ranges::size, views_));

26.7.24.3 Class template zip_view​::​iterator [range.zip.iterator]

namespace std::ranges { template<bool Const, class... Views> concept all-random-access = // exposition only (random_access_range<maybe-const<Const, Views>> && ...); template<bool Const, class... Views> concept all-bidirectional = // exposition only (bidirectional_range<maybe-const<Const, Views>> && ...); template<bool Const, class... Views> concept all-forward = // exposition only (forward_range<maybe-const<Const, Views>> && ...); template<input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) template<bool Const> class zip_view<Views...>::iterator { tuple<iterator_t<maybe-const<Const, Views>>...> current_; // exposition only constexpr explicit iterator(tuple<iterator_t<maybe-const<Const, Views>>...>); // exposition only public: using iterator_category = input_iterator_tag; // not always present using iterator_concept = see below; using value_type = tuple<range_value_t<maybe-const<Const, Views>>...>; using difference_type = common_type_t<range_difference_t<maybe-const<Const, Views>>...>; iterator() = default; constexpr iterator(iterator<!Const> i) requires Const && (convertible_to<iterator_t<Views>, iterator_t<const Views>> && ...); constexpr auto operator*() const; constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires all-forward<Const, Views...>; constexpr iterator& operator--() requires all-bidirectional<Const, Views...>; constexpr iterator operator--(int) requires all-bidirectional<Const, Views...>; constexpr iterator& operator+=(difference_type x) requires all-random-access<Const, Views...>; constexpr iterator& operator-=(difference_type x) requires all-random-access<Const, Views...>; constexpr auto operator[](difference_type n) const requires all-random-access<Const, Views...>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires (equality_comparable<iterator_t<maybe-const<Const, Views>>> && ...); friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires all-random-access<Const, Views...>; friend constexpr iterator operator+(const iterator& i, difference_type n) requires all-random-access<Const, Views...>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires all-random-access<Const, Views...>; friend constexpr iterator operator-(const iterator& i, difference_type n) requires all-random-access<Const, Views...>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires (sized_sentinel_for<iterator_t<maybe-const<Const, Views>>, iterator_t<maybe-const<Const, Views>>> && ...); friend constexpr auto iter_move(const iterator& i) noexcept(see below); friend constexpr void iter_swap(const iterator& l, const iterator& r) noexcept(see below) requires (indirectly_swappable<iterator_t<maybe-const<Const, Views>>> && ...); }; }
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iterator​::​iterator_concept is defined as follows:
  • (1.1)
    If all-random-access<Const, Views...> is modeled, then iterator_concept denotes random_access_iterator_tag.
  • (1.2)
    Otherwise, if all-bidirectional<Const, Views...> is modeled, then iterator_concept denotes bidirectional_iterator_tag.
  • (1.3)
    Otherwise, if all-forward<Const, Views...> is modeled, then iterator_concept denotes forward_iterator_tag.
  • (1.4)
    Otherwise, iterator_concept denotes input_iterator_tag.
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iterator​::​iterator_category is present if and only if all-forward<Const, Views...> is modeled.
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If the invocation of any non-const member function of iterator exits via an exception, the iterator acquires a singular value.
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constexpr explicit iterator(tuple<iterator_t<maybe-const<Const, Views>>...> current);
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Effects: Initializes current_ with std​::​move(current).
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constexpr iterator(iterator<!Const> i) requires Const && (convertible_to<iterator_t<Views>, iterator_t<const Views>> && ...);
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Effects: Initializes current_ with std​::​move(i.current_).
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constexpr auto operator*() const;
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Effects: Equivalent to: return tuple-transform([](auto& i) -> decltype(auto) { return *i; }, current_);
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constexpr iterator& operator++();
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Effects: Equivalent to: tuple-for-each([](auto& i) { ++i; }, current_); return *this;
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constexpr void operator++(int);
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Effects: Equivalent to ++*this.
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constexpr iterator operator++(int) requires all-forward<Const, Views...>;
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Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;
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constexpr iterator& operator--() requires all-bidirectional<Const, Views...>;
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Effects: Equivalent to: tuple-for-each([](auto& i) { --i; }, current_); return *this;
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constexpr iterator operator--(int) requires all-bidirectional<Const, Views...>;
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Effects: Equivalent to: auto tmp = *this; --*this; return tmp;
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constexpr iterator& operator+=(difference_type x) requires all-random-access<Const, Views...>;
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Effects: Equivalent to: tuple-for-each([&]<class I>(I& i) { i += iter_difference_t<I>(x); }, current_); return *this;
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constexpr iterator& operator-=(difference_type x) requires all-random-access<Const, Views...>;
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Effects: Equivalent to: tuple-for-each([&]<class I>(I& i) { i -= iter_difference_t<I>(x); }, current_); return *this;
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constexpr auto operator[](difference_type n) const requires all-random-access<Const, Views...>;
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Effects: Equivalent to: return tuple-transform([&]<class I>(I& i) -> decltype(auto) { return i[iter_difference_t<I>(n)]; }, current_);
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friend constexpr bool operator==(const iterator& x, const iterator& y) requires (equality_comparable<iterator_t<maybe-const<Const, Views>>> && ...);
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Returns:
  • (15.1)
    x.current_ == y.current_ if all-bidirectional<Const, Views...> is true.
  • (15.2)
    Otherwise, true if there exists an integer such that bool(std​::​​get<i>(x.current_) == std​::​get<i>(y.current_)) is true.
    [Note 1: 
    This allows zip_view to model common_range when all constituent views model common_range.
    — end note]
  • (15.3)
    Otherwise, false.
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friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires all-random-access<Const, Views...>;
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Returns: x.current_ <=> y.current_.
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friend constexpr iterator operator+(const iterator& i, difference_type n) requires all-random-access<Const, Views...>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires all-random-access<Const, Views...>;
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Effects: Equivalent to: auto r = i; r += n; return r;
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friend constexpr iterator operator-(const iterator& i, difference_type n) requires all-random-access<Const, Views...>;
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Effects: Equivalent to: auto r = i; r -= n; return r;
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friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires (sized_sentinel_for<iterator_t<maybe-const<Const, Views>>, iterator_t<maybe-const<Const, Views>>> && ...);
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Let DIST(i) be difference_type(std​::​get<i>(x.current_) - std​::​get<i>(y.current_)).
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Returns: The value with the smallest absolute value among DIST(n) for all integers .
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friend constexpr auto iter_move(const iterator& i) noexcept(see below);
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Effects: Equivalent to: return tuple-transform(ranges::iter_move, i.current_);
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Remarks: The exception specification is equivalent to: (noexcept(ranges::iter_move(declval<const iterator_t<maybe-const<Const, Views>>&>())) && ...) && (is_nothrow_move_constructible_v<range_rvalue_reference_t<maybe-const<Const, Views>>> && ...)
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friend constexpr void iter_swap(const iterator& l, const iterator& r) noexcept(see below) requires (indirectly_swappable<iterator_t<maybe-const<Const, Views>>> && ...);
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Effects: For every integer , performs: ranges::iter_swap(std::get<i>(l.current_), std::get<i>(r.current_))
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Remarks: The exception specification is equivalent to the logical and of the following expressions: noexcept(ranges::iter_swap(std::get<i>(l.current_), std::get<i>(r.current_))) for every integer .

26.7.24.4 Class template zip_view​::​sentinel [range.zip.sentinel]

namespace std::ranges { template<input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) template<bool Const> class zip_view<Views...>::sentinel { tuple<sentinel_t<maybe-const<Const, Views>>...> end_; // exposition only constexpr explicit sentinel(tuple<sentinel_t<maybe-const<Const, Views>>...> end); // exposition only public: sentinel() = default; constexpr sentinel(sentinel<!Const> i) requires Const && (convertible_to<sentinel_t<Views>, sentinel_t<const Views>> && ...); template<bool OtherConst> requires (sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires (sized_sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr common_type_t<range_difference_t<maybe-const<OtherConst, Views>>...> operator-(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires (sized_sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr common_type_t<range_difference_t<maybe-const<OtherConst, Views>>...> operator-(const sentinel& y, const iterator<OtherConst>& x); }; }
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constexpr explicit sentinel(tuple<sentinel_t<maybe-const<Const, Views>>...> end);
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Effects: Initializes end_ with end.
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constexpr sentinel(sentinel<!Const> i) requires Const && (convertible_to<sentinel_t<Views>, sentinel_t<const Views>> && ...);
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Effects: Initializes end_ with std​::​move(i.end_).
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template<bool OtherConst> requires (sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);
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Returns: true if there exists an integer such that bool(std​::​get<i>(x.​current_) == std​::​get<i>(y.end_)) is true.
Otherwise, false.
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template<bool OtherConst> requires (sized_sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr common_type_t<range_difference_t<maybe-const<OtherConst, Views>>...> operator-(const iterator<OtherConst>& x, const sentinel& y);
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Let D be the return type.
Let DIST(i) be D(std​::​get<i>(x.current_) - std​::​get<i>(y.end_)).
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Returns: The value with the smallest absolute value among DIST(n) for all integers .
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template<bool OtherConst> requires (sized_sentinel_for<sentinel_t<maybe-const<Const, Views>>, iterator_t<maybe-const<OtherConst, Views>>> && ...) friend constexpr common_type_t<range_difference_t<maybe-const<OtherConst, Views>>...> operator-(const sentinel& y, const iterator<OtherConst>& x);
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Effects: Equivalent to return -(x - y);