cppdraft_translate/cppdraft/range/adjacent/transform.md

[range.adjacent.transform]

25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.28 Adjacent transform view [range.adjacent.transform]

25.7.28.1 Overview [range.adjacent.transform.overview]

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adjacent_transform_view takes an invocable object and a view and produces a view whose Mth element is the result of applying the invocable object to the Mth through (M+N−1)th elements of the original view.

If the original view has fewer than N elements, the resulting view is empty.

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The name views​::​adjacent_transform denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F and a constant expression N:

• (2.1)

  If N is equal to 0 anddecltype((E)) models forward_range,views​::​adjacent_transform(E, F) is expression-equivalent to((void)E, views​::​zip_transform(F)), except that the evaluations of E and F are indeterminately sequenced.

• (2.2)

  Otherwise, the expression views​::​adjacent_transform(E, F) is expression-equivalent toadjacent_transform_view<views​::​all_t<decltype((E))>, decay_t<decltype((F))>, N>(E, F).

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[Example 1: vector v = {1, 2, 3, 4};

for (auto i : v | views::adjacent_transform<2>(std::multiplies())) { cout << i << ' '; // prints 2 6 12} — end example]

25.7.28.2 Class template adjacent_transform_view [range.adjacent.transform.view]

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namespace std::ranges {template<forward_range V, move_constructible F, size_t N>requires view && (N > 0) && is_object_v &&regular_invocable<F&, REPEAT(range_reference_t, N)...> &&can-reference<invoke_result_t<F&, REPEAT(range_reference_t, N)...>>class adjacent_transform_view : public view_interface<adjacent_transform_view<V, F, N>> {movable-box fun_; // exposition only adjacent_view<V, N> inner_; // exposition onlyusing InnerView = adjacent_view<V, N>; // exposition onlytemplateusing inner-iterator = iterator_t<maybe-const<Const, InnerView>>; // exposition onlytemplateusing inner-sentinel = sentinel_t<maybe-const<Const, InnerView>>; // exposition only// [range.adjacent.transform.iterator], class template adjacent_transform_view​::​iteratortemplate class iterator; // exposition only// [range.adjacent.transform.sentinel], class template adjacent_transform_view​::​sentineltemplate class sentinel; // exposition onlypublic: adjacent_transform_view() = default; constexpr explicit adjacent_transform_view(V base, F fun); constexpr V base() const & requires copy_constructible { return inner_.base(); }constexpr V base() && { return std::move(inner_).base(); }constexpr auto begin() {return iterator(*this, inner_.begin()); }constexpr auto begin() constrequires range<const InnerView> &&regular_invocable<const F&, REPEAT(range_reference_t, N)...> {return iterator(*this, inner_.begin()); }constexpr auto end() {if constexpr (common_range<InnerView>) {return iterator(*this, inner_.end()); } else {return sentinel(inner_.end()); }}constexpr auto end() constrequires range<const InnerView> &&regular_invocable<const F&, REPEAT(range_reference_t, N)...> {if constexpr (common_range<const InnerView>) {return iterator(*this, inner_.end()); } else {return sentinel(inner_.end()); }}constexpr auto size() requires sized_range<InnerView> {return inner_.size(); }constexpr auto size() const requires sized_range<const InnerView> {return inner_.size(); }constexpr auto reserve_hint() requires approximately_sized_range<InnerView> {return inner_.reserve_hint(); }constexpr auto reserve_hint() const requires approximately_sized_range<const InnerView> {return inner_.reserve_hint(); }};}

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constexpr explicit adjacent_transform_view(V base, F fun);

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Effects: Initializes fun_ with std​::​move(fun) andinner_ with std​::​move(base).

25.7.28.3 Class template adjacent_transform_view​::​iterator [range.adjacent.transform.iterator]

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namespace std::ranges {template<forward_range V, move_constructible F, size_t N>requires view && (N > 0) && is_object_v &&regular_invocable<F&, REPEAT(range_reference_t, N)...> &&can-reference<invoke_result_t<F&, REPEAT(range_reference_t, N)...>>templateclass adjacent_transform_view<V, F, N>::iterator {using Parent = maybe-const<Const, adjacent_transform_view>; // exposition onlyusing Base = maybe-const<Const, V>; // exposition onlyParent parent_ = nullptr; // exposition only**inner-iterator inner_; // exposition onlyconstexpr iterator(Parent& parent, inner-iterator inner); // exposition onlypublic:using iterator_category = see below; using iterator_concept = typename inner-iterator::iterator_concept; using value_type = remove_cvref_t<invoke_result_t<maybe-const<Const, F>&, REPEAT(range_reference_t<Base>, N)...>>; using difference_type = range_difference_t<Base>; iterator() = default; constexpr iterator(iterator i)requires Const && convertible_to<inner-iterator, inner-iterator>; constexpr decltype(auto) operator() const noexcept(see below); constexpr iterator& operator++(); constexpr iterator operator++(int); 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); friend constexpr bool operator<(const iterator& x, const iterator& y)requires random_access_range<Base>; friend constexpr bool operator>(const iterator& x, const iterator& y)requires random_access_range<Base>; friend constexpr bool operator<=(const iterator& x, const iterator& y)requires random_access_range<Base>; friend constexpr bool operator>=(const iterator& x, const iterator& y)requires random_access_range<Base>; friend constexpr auto operator<=>(const iterator& x, const iterator& y)requires random_access_range<Base> && three_way_comparable<inner-iterator>; 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<inner-iterator, inner-iterator>; };}

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The member typedef-name iterator​::​iterator_category is defined as follows:

• (1.1)

  If invoke_result_t<maybe-const<Const, F>&,REPEAT(range_reference_t<Base>, N)...> is not a reference,iterator_category denotes input_iterator_tag.

• (1.2)

  Otherwise, let C denote the typeiterator_traits<iterator_t<Base>>​::​iterator_category.

  • (1.2.1)

    If derived_from<C, random_access_iterator_tag> is true,iterator_category denotes random_access_iterator_tag.

  • (1.2.2)

    Otherwise, if derived_from<C, bidirectional_iterator_tag> is true,iterator_category denotes bidirectional_iterator_tag.

  • (1.2.3)

    Otherwise, if derived_from<C, 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, inner-iterator<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]")<inner-iterator<false>, inner-iterator<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, …, (N - 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 iterator operator++(int);

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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([&](const auto&... iters) -> decltype(auto) {return invoke(**parent_*->fun_, iters[n]...);}, inner_.current_);

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friend constexpr bool operator==(const iterator& x, const iterator& y); friend constexpr bool 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>; friend constexpr bool 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>; friend constexpr bool 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>; friend constexpr bool 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>; 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> && [three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<inner-iterator<Const>>;

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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]")<inner-iterator<Const>, inner-iterator<Const>>;

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Effects: Equivalent to: return x.inner_ - y.inner_;

25.7.28.4 Class template adjacent_transform_view​::​sentinel [range.adjacent.transform.sentinel]

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namespace std::ranges {template<forward_range V, move_constructible F, size_t N>requires view && (N > 0) && is_object_v &&regular_invocable<F&, REPEAT(range_reference_t, N)...> &&can-reference<invoke_result_t<F&, REPEAT(range_reference_t, N)...>>templateclass adjacent_transform_view<V, F, N>::sentinel {inner-sentinel inner_; // exposition onlyconstexpr explicit sentinel(inner-sentinel inner); // exposition onlypublic:sentinel() = default; constexpr sentinel(sentinel i)requires Const && convertible_to<inner-sentinel, inner-sentinel>; templaterequires sentinel_for<inner-sentinel, inner-iterator>friend constexpr bool operator==(const iterator& x, const sentinel& y); templaterequires sized_sentinel_for<inner-sentinel, inner-iterator>friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>>operator-(const iterator& x, const sentinel& y); templaterequires sized_sentinel_for<inner-sentinel, inner-iterator>friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>>operator-(const sentinel& x, const iterator& y); };}

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constexpr explicit sentinel(inner-sentinel<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]")<inner-sentinel<false>, inner-sentinel<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]")<inner-sentinel<Const>, inner-iterator<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 requires sized_sentinel_for<inner-sentinel, inner-iterator> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const iterator& x, const sentinel& y);

template requires sized_sentinel_for<inner-sentinel, inner-iterator> friend constexpr range_difference_t<maybe-const<OtherConst, InnerView>> operator-(const sentinel& x, const iterator& y); `

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Effects: Equivalent to: return x.inner_ - y.inner_;