cppdraft_translate/cppdraft/range/zip/transform.md

[range.zip.transform]

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 Mth element is the result of applying the invocable object to the Mth 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 &&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 && ...) && (sizeof...(Views) > 0) && is_object_v &&regular_invocable<F&, range_reference_t...> &&can-reference<invoke_result_t<F&, range_reference_t...>>class zip_transform_view : public view_interface<zip_transform_view<F, Views...>> {movable-box fun_; // exposition only zip_view<Views...> zip_; // exposition onlyusing InnerView = zip_view<Views...>; // exposition onlytemplateusing ziperator = iterator_t<maybe-const<Const, InnerView>>; // exposition onlytemplateusing zentinel = sentinel_t<maybe-const<Const, InnerView>>; // exposition only// [range.zip.transform.iterator], class template zip_transform_view​::​iteratortemplate class iterator; // exposition only// [range.zip.transform.sentinel], class template zip_transform_view​::​sentineltemplate class sentinel; // exposition onlypublic: zip_transform_view() = default; constexpr explicit zip_transform_view(F fun, Views... views); constexpr auto begin() { return iterator(*this, zip_.begin()); }constexpr auto begin() constrequires range<const InnerView> &&regular_invocable<const F&, range_reference_t...> {return iterator(*this, zip_.begin()); }constexpr auto end() {if constexpr (common_range<InnerView>) {return iterator(*this, zip_.end()); } else {return sentinel(zip_.end()); }}constexpr auto end() constrequires range<const InnerView> &&regular_invocable<const F&, range_reference_t...> {if constexpr (common_range<const InnerView>) {return iterator(*this, zip_.end()); } else {return sentinel(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...>;}

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constexpr explicit zip_transform_view(F fun, Views... views);

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Effects: Initializes fun_ with std​::​move(fun) andzip_ with std​::​move(views)....

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

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namespace std::ranges {template<move_constructible F, input_range... Views>requires (view && ...) && (sizeof...(Views) > 0) && is_object_v &&regular_invocable<F&, range_reference_t...> &&can-reference<invoke_result_t<F&, range_reference_t...>>templateclass zip_transform_view<F, Views...>::iterator {using Parent = maybe-const<Const, zip_transform_view>; // exposition onlyusing Base = maybe-const<Const, InnerView>; // exposition onlyParent parent_ = nullptr; // exposition only**ziperator inner_; // exposition onlyconstexpr iterator(Parent& parent, ziperator inner); // exposition onlypublic:using iterator_category = see below; // not always presentusing iterator_concept = typename ziperator::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 i)requires Const && convertible_to<ziperator, ziperator>; 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) constrequires random_access_range<Base>; friend constexpr bool operator==(const iterator& x, const iterator& y)requires equality_comparable<ziperator>; 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, ziperator>; };}

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The member typedef-nameiterator​::​iterator_category is defined if and only if Base models forward_range.

In that case,iterator​::​iterator_category is defined as follows:

• (1.1)

Ifinvoke_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 typesiterator_traits<iterator_t<maybe-const<Const, Views>>>​::​iterator_category.... * (1.2.1)

  If ([derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<Cs, random_access_iterator_tag> && ...) is true,iterator_category denotes random_access_iterator_tag[.](#iterator-1.2.1.sentence-1)

• (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) andinner_ with std​::​move(inner).

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constexpr iterator(iterator<!Const> i) requires Const && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<ziperator<false>, ziperator<Const>>;

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Effects: Initializes parent_ with i.parent_ andinner_ 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(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](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to:auto tmp = *this;++*this;return tmp;

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constexpr iterator& operator--() requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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Effects: Equivalent to:--inner_;return *this;

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constexpr iterator operator--(int) requires [bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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(n)]...);}, inner_.current_);

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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]")<ziperator<Const>>; friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>;

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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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<Base>; friend constexpr iterator operator+(difference_type n, const iterator& i) requires [random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]")<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](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<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]

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namespace std::ranges {template<move_constructible F, input_range... Views>requires (view && ...) && (sizeof...(Views) > 0) && is_object_v &&regular_invocable<F&, range_reference_t...> &&can-reference<invoke_result_t<F&, range_reference_t...>>templateclass zip_transform_view<F, Views...>::sentinel {zentinel inner_; // exposition onlyconstexpr explicit sentinel(zentinel inner); // exposition onlypublic:sentinel() = default; constexpr sentinel(sentinel i)requires Const && convertible_to<zentinel, zentinel>; templaterequires sentinel_for<zentinel, ziperator>friend constexpr bool operator==(const iterator& x, const sentinel& y); templaterequires sized_sentinel_for<zentinel, ziperator>friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>>operator-(const iterator& x, const sentinel& y); templaterequires sized_sentinel_for<zentinel, ziperator>friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>>operator-(const sentinel& x, const iterator& 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](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<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](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<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](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<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](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<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_;