# std::ranges::views::adjacent_transform, std::ranges::adjacent_transform_view, std::ranges::views::pairwise_transform

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< cpp‎ | ranges

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 > inline 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 `i`th 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​ (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.

`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.

### Data members

Typical implementations of `adjacent_transform_view` hold two non-static data members:

- `fun_` of type __movable_box<F>,
- `inner_` of type ranges::adjacent_view<V,N>

These names are for exposition only.

### Member functions

(constructor) (C++23) | constructs a `adjacent_transform_view` (public member function)
begin (C++23) | returns an iterator to the beginning (public member function)
end (C++23) | returns an iterator or a sentinel to the end (public member function)
size (C++23) | returns the number of elements. Provided only if the underlying (adapted) range satisfies `sized_range`. (public member function)
##### Inherited from std::ranges::view_interface
empty (C++20) | returns whether the derived view is empty. Provided if it satisfies `sized_range` or `forward_range`. (public member function of `std::ranges::view_interface<D>`)
cbegin (C++23) | returns a constant iterator to the beginning of the range. (public member function of `std::ranges::view_interface<D>`)
cend (C++23) | returns a sentinel for the constant iterator of the range. (public member function of `std::ranges::view_interface<D>`)
operator bool (C++20) | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of `std::ranges::view_interface<D>`)
front (C++20) | returns the first element in the derived view. Provided if it satisfies `forward_range`. (public member function of `std::ranges::view_interface<D>`)
back (C++20) | returns the last element in the derived view. Provided if it satisfies `bidirectional_range` and `common_range`. (public member function of `std::ranges::view_interface<D>`)
operator[] (C++20) | returns the nth element in the derived view. Provided if it satisfies `random_access_range`. (public member function of `std::ranges::view_interface<D>`)

### Deduction guides

(none)

### Member types

Member type | Definition
`InnerView` (private) | ranges::adjacent_view<V, N>. The name is for exposition only.
`inner_iterator` (private) | ranges::iterator_t<const InnerView>, if Const is true. Otherwise, ranges::iterator_t<InnerView>. The name is for exposition only.
`inner_sentinel` (private) | ranges::sentinel_t<const InnerView>, if Const is true. Otherwise, ranges::sentinel_t<InnerView>. The name is for exposition only.

### Nested classes

iterator (C++23) | the iterator type (exposition-only member class template*)
sentinel (C++23) | the sentinel type used when `adjacent_transform_view` is not a `common_range` (exposition-only member class template*)

### Notes

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

### Example

A link to test: Compiler Explorer/g++-13

Run this code

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

    int main()
    {
        constexpr static auto source = {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 = source | std::views::adjacent_transform< window >(Fun);

        static_assert(
            view.size() == (source.size() - window + 1)
            and
            std::array{view[0], view[1], view[2], view[3]} == std::array{6, 9, 12, 15}
        );

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

Output:

    6 9 12 15

### References

- C++23 standard (ISO/IEC 14882:2023):

  - 26.7.27 Adjacent transform view [range.adjacent.transform]

### See also

ranges::adjacent_view views::adjacent (C++23) | a `view` consisting of tuples of references to adjacent elements of the adapted view (class template) (range adaptor object)
ranges::transform_view views::transform (C++20) | a `view` of a sequence that applies a transformation function to each element (class template) (range adaptor object)
ranges::zip_transform_view views::zip_transform (C++23) | a `view` consisting of tuples of results of application of a transformation function to corresponding elements of the adapted views (class template) (customization point object)
ranges::transform (C++20) | applies a function to a range of elements (niebloid)

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