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 element is the result of applying the invocable object to the through 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<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 and decltype((E)) models forward_range, 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).
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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<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<V> { 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);
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Effects: Initializes fun_ with std​::​move(fun) and inner_ with std​::​move(base).

25.7.28.3 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>>; }; }
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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 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);
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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<inner-iterator<false>, inner-iterator<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, …, (N-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 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<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([&](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>>;
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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<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]

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>::sentinel { inner-sentinel<Const> inner_; // exposition only constexpr explicit sentinel(inner-sentinel<Const> inner); // exposition only public: sentinel() = default; constexpr sentinel(sentinel<!Const> i) requires Const && convertible_to<inner-sentinel<false>, inner-sentinel<Const>>; template<bool OtherConst> requires sentinel_for<inner-sentinel<Const>, inner-iterator<OtherConst>> friend constexpr bool 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 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); }; }
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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<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<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<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);
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Effects: Equivalent to: return x.inner_ - y.inner_;