26 Ranges library [ranges]

26.7 Range adaptors [range.adaptors]

26.7.27 Adjacent transform view [range.adjacent.transform]

26.7.27.1 Overview [range.adjacent.transform.overview]

adjacent_transform_view takes an invocable object and a view and produces a view whose

M^{th}

element is the result of applying the invocable object to the

M^{th}

through

(M + N - 1)^{th}

elements of the original view.

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

The name views::adjacent_transform<N> 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, views::adjacent_transform<N>(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<N>(E, F) is expression-equivalent to adjacent_transform_view<views::all_t<decltype((E))>, decay_t<decltype((F))>, N>(E, F).

[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]

26.7.27.2 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<V> && (N > 0) && is_object_v<F> && regular_invocable<F&, REPEAT(range_reference_t<V>, N)...> && can-reference<invoke_result_t<F&, REPEAT(range_reference_t<V>, N)...>> class adjacent_transform_view : public view_interface<adjacent_transform_view<V, F, N>> { movable-box<F> fun_; // exposition only adjacent_view<V, N> inner_; // exposition only using InnerView = adjacent_view<V, N>; // exposition only template<bool Const> using inner-iterator = iterator_t<maybe-const<Const, InnerView>>; // exposition only template<bool Const> using inner-sentinel = sentinel_t<maybe-const<Const, InnerView>>; // exposition only // [range.adjacent.transform.iterator], class template adjacent_transform_view::iterator template<bool> class iterator; // exposition only // [range.adjacent.transform.sentinel], class template adjacent_transform_view::sentinel template<bool> class sentinel; // exposition only public: adjacent_transform_view() = default; constexpr explicit adjacent_transform_view(V base, F fun); constexpr V base() const & requires copy_constructible<InnerView> { return inner_.base(); } constexpr V base() && { return std::move(inner_).base(); } constexpr auto begin() { return iterator<false>(*this, inner_.begin()); } constexpr auto begin() const requires range<const InnerView> && regular_invocable<const F&, REPEAT(range_reference_t<const V>, N)...> { return iterator<true>(*this, inner_.begin()); } constexpr auto end() { if constexpr (common_range<InnerView>) { return iterator<false>(*this, inner_.end()); } else { return sentinel<false>(inner_.end()); } } constexpr auto end() const requires range<const InnerView> && regular_invocable<const F&, REPEAT(range_reference_t<const V>, N)...> { if constexpr (common_range<const InnerView>) { return iterator<true>(*this, inner_.end()); } else { return sentinel<true>(inner_.end()); } } constexpr auto size() requires sized_range<InnerView> { return inner_.size(); } constexpr auto size() const requires sized_range<const InnerView> { return inner_.size(); } }; }

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constexpr explicit adjacent_transform_view(V base, F fun);

Effects: Initializes fun_ with std::move(fun) and inner_ with std::move(base).

26.7.27.3 Class template adjacent_transform_view::iterator [range.adjacent.transform.iterator]

namespace std::ranges { template<forward_range V, move_constructible F, size_t N> requires view<V> && (N > 0) && is_object_v<F> && regular_invocable<F&, REPEAT(range_reference_t<V>, N)...> && can-reference<invoke_result_t<F&, REPEAT(range_reference_t<V>, N)...>> template<bool Const> class adjacent_transform_view<V, F, N>::iterator { using Parent = maybe-const<Const, adjacent_transform_view>; // exposition only using Base = maybe-const<Const, V>; // exposition only Parent* parent_ = nullptr; // exposition only inner-iterator<Const> inner_; // exposition only constexpr iterator(Parent& parent, inner-iterator<Const> inner); // exposition only public: using iterator_category = see below; using iterator_concept = typename inner-iterator<Const>::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<!Const> i) requires Const && convertible_to<inner-iterator<false>, inner-iterator<Const>>; 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) const requires 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<Const>>; 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<Const>, inner-iterator<Const>>; }; }

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 type iterator_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);

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<inner-iterator<false>, inner-iterator<Const>>;

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);

Effects: Equivalent to: return apply([&](const auto&... iters) -> decltype(auto) { return invoke(*parent_->fun_, *iters...); }, inner_.current_);

Remarks: Let Is be the pack 0, 1, …, (N-1).

The exception specification is equivalent to: noexcept(invoke(*parent_->fun_, *std::get<Is>(inner_.current_)...))

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constexpr iterator& operator++();

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

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constexpr iterator operator++(int);

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

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constexpr iterator& operator--() requires bidirectional_range<Base>;

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

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constexpr iterator operator--(int) requires bidirectional_range<Base>;

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

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constexpr iterator& operator+=(difference_type x) requires random_access_range<Base>;

Effects: Equivalent to: inner_ += x; return *this;

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constexpr iterator& operator-=(difference_type x) requires random_access_range<Base>;

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

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constexpr decltype(auto) operator[](difference_type n) const
  requires random_access_range<Base>;

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<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<Const>>;

Let op be the operator.

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>;

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>;

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<inner-iterator<Const>, inner-iterator<Const>>;

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

26.7.27.4 Class template adjacent_transform_view::sentinel [range.adjacent.transform.sentinel]

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constexpr explicit sentinel(inner-sentinel<Const> inner);

Effects: Initializes inner_ with inner.

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constexpr sentinel(sentinel<!Const> i)
  requires Const && convertible_to<inner-sentinel<false>, inner-sentinel<Const>>;

Effects: Initializes inner_ with std::move(i.inner_).

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template<bool OtherConst>
  requires sentinel_for<inner-sentinel<Const>, inner-iterator<OtherConst>>
friend constexpr bool operator==(const iterator<OtherConst>& x, const sentinel& y);

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

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

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