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std::ranges::views::adjacent_transform, std::ranges::adjacent_transform_view, std::ranges::views::pairwise_transform - cppreference.com

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Defined in header <ranges>

template< ranges::forward_range V, std::move_constructible F, std::size_t N > requires ranges::view<V> && (N > 0) && std::is_object_v<F> && std::regular_invocable<F&, /*REPEAT*/(ranges::range_reference_t<V>, N)...> && /*can-reference*/<std::invoke_result_t<F&, /*REPEAT*/(ranges::range_reference_t<V>, N)...>> class adjacent_transform_view : public ranges::view_interface<adjacent_transform_view<V, F, N>>

 (1) (since C++23)

namespace views { template< std::size_t N > constexpr /* unspecified */ adjacent_transform = /* unspecified */; }

 (2) (since C++23)

namespace views { inline constexpr auto pairwise_transform = adjacent_transform<2>; }

 (3) (since C++23)

Call signature

template< ranges::viewable_range R, class F > requires /* see below */ constexpr ranges::view auto adjacent_transform<N>( R&& r, F&& fun );

 (since C++23)

template< class F > constexpr /*range adaptor closure*/ adjacent_transform<N>( F&& fun );

 (since C++23)

1) adjacent_transform_view is a range adaptor that takes a view and an invocable object fun, and produces a view whose ith element is a value that is the result of applying fun to each element in [i, i + N) of the original view. F always has arity N.

Let S be the size of the original view. Then the size of produced view is:

  • S - N + 1, if S >= N,
  • 0 otherwise, and the resulting view is empty.

2) The name views::adjacent_transform<N> denotes a RangeAdaptorObject. Given subexpressions e and f, and a constant expression N, the expression views::adjacent_transform<N>(e, f) is expression-equivalent to:

  • ((void)e, views::zip_transform(f)), if N is equal to 0 and decltype((e)) models forward_range (except that the evaluations of e and f are indeterminately sequenced),
  • adjacent_transform_view<views::all_t<decltype((e))>, std::decay_t<decltype((f))>, N>(e, f) otherwise.

3) The name views::pairwise_transform denotes a RangeAdaptorObject that behaves exactly as views::adjacent_transform<2>. In particular, the arity of F is also 2 and fun is a binary invocable object.

adjacent_transform_view always models forward_range, and models bidirectional_range, random_access_range, or sized_range, if adapted view type models the corresponding concept.

Member functions

constructs a adjacent_transform_view
(public member function) [edit]
returns an iterator to the beginning
(public member function) [edit]
returns an iterator or a sentinel to the end
(public member function) [edit]
returns the number of elements, provided only if the underlying (adapted) range satisfies sized_range
(public member function) [edit]
returns the approximate size of the resulting approximately_sized_range
(public member function) [edit]
Inherited from ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the nth element in the derived view, provided only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit]

Nested types

Type Definition
InnerView (private) ranges::adjacent_view<V, N>
(exposition-only member type*)
inner_iterator (private)
  • ranges::iterator_t<const InnerView>, if Const is true. Otherwise,
  • ranges::iterator_t<InnerView>
    (exposition-only member type*)
inner_sentinel (private)
  • ranges::sentinel_t<const InnerView>, if Const is true. Otherwise,
  • ranges::sentinel_t<InnerView>
    (exposition-only member type*)

Data members

Member Description
/*movable-box*/<F> fun_ (private) the transforming invocable object
(exposition-only member object*)
ranges::adjacent_view<V,N> inner_ (private) the stored view
(exposition-only member object*)

Nested classes

the iterator type
(exposition-only member class template*)
the sentinel type used when adjacent_transform_view is not a common_range
(exposition-only member class template*)

Notes

views::adjacent_transform only accepts foward ranges even when N is 0.

Feature-test macro Value Std Feature
__cpp_lib_ranges_zip 202110L (C++23) ranges::zip_view,
ranges::zip_transform_view,
ranges::adjacent_view,
ranges::adjacent_transform_view

Example

#include <array>
#include <iostream>
#include <ranges>

int main()
{
    constexpr static std::array data{1, 2, 3, 4, 5, 6};
    constexpr int window{3};

    auto Fun = [](auto... ints) { return (... + ints); };
    // Alternatively, the Fun could be any ternary (if window == 3) callable, e.g.:
    // auto Fun = [](int x, int y, int z) { return x + y + z; };

    constexpr auto view = data | std::views::adjacent_transform<window>(Fun);

    static_assert(
        view.size() == (data.size() - window + 1)
        && std::array{6, 9, 12, 15}
        == std::array{view[0], view[1], view[2], view[3]}
        && view[0] == Fun(data[0], data[1], data[2])
        && view[1] == Fun(data[1], data[2], data[3])
        && view[2] == Fun(data[2], data[3], data[4])
        && view[3] == Fun(data[3], data[4], data[5])
    );

    for (int x : view)
        std::cout << x << ' ';
    std::cout << '\n';
}

Output:

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 4098 C++23 views::adjacent_transform<0> used to accept input-only ranges made rejected

References

  • C++23 standard (ISO/IEC 14882:2024):
  • 26.7.27 Adjacent transform view [range.adjacent.transform]

See also