25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.26 Zip transform view [range.zip.transform]

25.7.26.1 Overview [range.zip.transform.overview]

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zip_transform_view takes an invocable object and any number of views and produces a view whose element is the result of applying the invocable object to the elements of all views.
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The name views​::​zip_transform denotes a customization point object ([customization.point.object]).
Let F be a subexpression, and let Es... be a pack of subexpressions.
  • (2.1)
    If Es is an empty pack, let FD be decay_t<decltype((F))>.
    • (2.1.1)
      If move_constructible<FD> && regular_invocable<FD&> is false, or if decay_t<invoke_result_t<FD&>> is not an object type, views​::​zip_transform(F, Es...) is ill-formed.
    • (2.1.2)
      Otherwise, the expression views​::​zip_transform(F, Es...) is expression-equivalent to ((void)F, auto(views::empty<decay_t<invoke_result_t<FD&>>>))
  • (2.2)
    Otherwise, the expression views​::​zip_transform(F, Es...) is expression-equivalent to zip_transform_view(F, Es...).
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[Example 1: vector v1 = {1, 2}; vector v2 = {4, 5, 6}; for (auto i : views::zip_transform(plus(), v1, v2)) { cout << i << ' '; // prints 5 7 } — end example]

25.7.26.2 Class template zip_transform_view [range.zip.transform.view]

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namespace std::ranges { template<move_constructible F, input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> && regular_invocable<F&, range_reference_t<Views>...> && can-reference<invoke_result_t<F&, range_reference_t<Views>...>> class zip_transform_view : public view_interface<zip_transform_view<F, Views...>> { movable-box<F> fun_; // exposition only zip_view<Views...> zip_; // exposition only using InnerView = zip_view<Views...>; // exposition only template<bool Const> using ziperator = iterator_t<maybe-const<Const, InnerView>>; // exposition only template<bool Const> using zentinel = sentinel_t<maybe-const<Const, InnerView>>; // exposition only // [range.zip.transform.iterator], class template zip_transform_view​::​iterator template<bool> class iterator; // exposition only // [range.zip.transform.sentinel], class template zip_transform_view​::​sentinel template<bool> class sentinel; // exposition only public: zip_transform_view() = default; constexpr explicit zip_transform_view(F fun, Views... views); constexpr auto begin() { return iterator<false>(*this, zip_.begin()); } constexpr auto begin() const requires range<const InnerView> && regular_invocable<const F&, range_reference_t<const Views>...> { return iterator<true>(*this, zip_.begin()); } constexpr auto end() { if constexpr (common_range<InnerView>) { return iterator<false>(*this, zip_.end()); } else { return sentinel<false>(zip_.end()); } } constexpr auto end() const requires range<const InnerView> && regular_invocable<const F&, range_reference_t<const Views>...> { if constexpr (common_range<const InnerView>) { return iterator<true>(*this, zip_.end()); } else { return sentinel<true>(zip_.end()); } } constexpr auto size() requires sized_range<InnerView> { return zip_.size(); } constexpr auto size() const requires sized_range<const InnerView> { return zip_.size(); } }; template<class F, class... Rs> zip_transform_view(F, Rs&&...) -> zip_transform_view<F, views::all_t<Rs>...>; }
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constexpr explicit zip_transform_view(F fun, Views... views);
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Effects: Initializes fun_ with std​::​move(fun) and zip_ with std​::​move(views)....

25.7.26.3 Class template zip_transform_view​::​iterator [range.zip.transform.iterator]

namespace std::ranges { template<move_constructible F, input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> && regular_invocable<F&, range_reference_t<Views>...> && can-reference<invoke_result_t<F&, range_reference_t<Views>...>> template<bool Const> class zip_transform_view<F, Views...>::iterator { using Parent = maybe-const<Const, zip_transform_view>; // exposition only using Base = maybe-const<Const, InnerView>; // exposition only Parent* parent_ = nullptr; // exposition only ziperator<Const> inner_; // exposition only constexpr iterator(Parent& parent, ziperator<Const> inner); // exposition only public: using iterator_category = see below; // not always present using iterator_concept = typename ziperator<Const>::iterator_concept; using value_type = remove_cvref_t<invoke_result_t<maybe-const<Const, F>&, range_reference_t<maybe-const<Const, Views>>...>>; using difference_type = range_difference_t<Base>; iterator() = default; constexpr iterator(iterator<!Const> i) requires Const && convertible_to<ziperator<false>, ziperator<Const>>; constexpr decltype(auto) operator*() const noexcept(see below); constexpr iterator& operator++(); constexpr void operator++(int); constexpr iterator operator++(int) requires forward_range<Base>; constexpr iterator& operator--() requires bidirectional_range<Base>; constexpr iterator operator--(int) requires bidirectional_range<Base>; constexpr iterator& operator+=(difference_type x) requires random_access_range<Base>; constexpr iterator& operator-=(difference_type x) requires random_access_range<Base>; constexpr decltype(auto) operator[](difference_type n) const requires random_access_range<Base>; friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<ziperator<Const>>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires random_access_range<Base>; friend constexpr iterator operator+(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires random_access_range<Base>; friend constexpr iterator operator-(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires sized_sentinel_for<ziperator<Const>, ziperator<Const>>; }; }
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The member typedef-name iterator​::​iterator_category is defined if and only if Base models forward_range.
In that case, iterator​::​iterator_category is defined as follows:
  • (1.1)
    If invoke_result_t<maybe-const<Const, F>&, range_reference_t<maybe-const<Const, Views>>...> is not a reference, iterator_category denotes input_iterator_tag.
  • (1.2)
    Otherwise, let Cs denote the pack of types iterator_traits<iterator_t<maybe-const<Const, Views>>>​::​iterator_category....
    • (1.2.1)
      If (derived_from<Cs, random_access_iterator_tag> && ...) is true, iterator_category denotes random_access_iterator_tag.
    • (1.2.2)
      Otherwise, if (derived_from<Cs, bidirectional_iterator_tag> && ...) is true, iterator_category denotes bidirectional_iterator_tag.
    • (1.2.3)
      Otherwise, if (derived_from<Cs, forward_iterator_tag> && ...) is true, iterator_category denotes forward_iterator_tag.
    • (1.2.4)
      Otherwise, iterator_category denotes input_iterator_tag.
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constexpr iterator(Parent& parent, ziperator<Const> inner);
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Effects: Initializes parent_ with addressof(parent) and inner_ with std​::​move(inner).
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constexpr iterator(iterator<!Const> i) requires Const && convertible_to<ziperator<false>, ziperator<Const>>;
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Effects: Initializes parent_ with i.parent_ and inner_ with std​::​move(i.inner_).
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constexpr decltype(auto) operator*() const noexcept(see below);
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Effects: Equivalent to: return apply([&](const auto&... iters) -> decltype(auto) { return invoke(*parent_->fun_, *iters...); }, inner_.current_);
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Remarks: Let Is be the pack 0, 1, …, (sizeof...(Views)-1).
The exception specification is equivalent to: noexcept(invoke(*parent_->fun_, *std​::​get<Is>(inner_.current_)...)).
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constexpr iterator& operator++();
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Effects: Equivalent to: ++inner_; 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 forward_range<Base>;
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Effects: Equivalent to: auto tmp = *this; ++*this; return tmp;
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constexpr iterator& operator--() requires bidirectional_range<Base>;
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Effects: Equivalent to: --inner_; return *this;
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constexpr iterator operator--(int) requires bidirectional_range<Base>;
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Effects: Equivalent to: auto tmp = *this; --*this; return tmp;
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constexpr iterator& operator+=(difference_type x) requires random_access_range<Base>;
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Effects: Equivalent to: inner_ += x; return *this;
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constexpr iterator& operator-=(difference_type x) requires random_access_range<Base>;
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Effects: Equivalent to: inner_ -= x; return *this;
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constexpr decltype(auto) operator[](difference_type n) const requires random_access_range<Base>;
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Effects: Equivalent to: return apply([&]<class... Is>(const Is&... iters) -> decltype(auto) { return invoke(*parent_->fun_, iters[iter_difference_t<Is>(n)]...); }, inner_.current_);
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friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<ziperator<Const>>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires random_access_range<Base>;
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Let op be the operator.
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Effects: Equivalent to: return x.inner_ op y.inner_;
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friend constexpr iterator operator+(const iterator& i, difference_type n) requires random_access_range<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires random_access_range<Base>;
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Effects: Equivalent to: return iterator(*i.parent_, i.inner_ + n);
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friend constexpr iterator operator-(const iterator& i, difference_type n) requires random_access_range<Base>;
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Effects: Equivalent to: return iterator(*i.parent_, i.inner_ - n);
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friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires sized_sentinel_for<ziperator<Const>, ziperator<Const>>;
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Effects: Equivalent to: return x.inner_ - y.inner_;

25.7.26.4 Class template zip_transform_view​::​sentinel [range.zip.transform.sentinel]

namespace std::ranges { template<move_constructible F, input_range... Views> requires (view<Views> && ...) && (sizeof...(Views) > 0) && is_object_v<F> && regular_invocable<F&, range_reference_t<Views>...> && can-reference<invoke_result_t<F&, range_reference_t<Views>...>> template<bool Const> class zip_transform_view<F, Views...>::sentinel { zentinel<Const> inner_; // exposition only constexpr explicit sentinel(zentinel<Const> inner); // exposition only public: sentinel() = default; constexpr sentinel(sentinel<!Const> i) requires Const && convertible_to<zentinel<false>, zentinel<Const>>; template<bool OtherConst> requires sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires sized_sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires sized_sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const sentinel& x, const iterator<OtherConst>& y); }; }
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constexpr explicit sentinel(zentinel<Const> inner);
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Effects: Initializes inner_ with inner.
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constexpr sentinel(sentinel<!Const> i) requires Const && convertible_to<zentinel<false>, zentinel<Const>>;
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Effects: Initializes inner_ with std​::​move(i.inner_).
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template<bool OtherConst> requires sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);
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Effects: Equivalent to: return x.inner_ == y.inner_;
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template<bool OtherConst> requires sized_sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const iterator<OtherConst>& x, const sentinel& y); template<bool OtherConst> requires sized_sentinel_for<zentinel<Const>, ziperator<OtherConst>> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const sentinel& x, const iterator<OtherConst>& y);
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Effects: Equivalent to: return x.inner_ - y.inner_;