std::ranges...sform_view,(3)

📦 version 2024.07.05, in nixpkgs unstable, opensuse-leap 16.0

🎀 std::ranges...sform_view,(3) 🎀

hey bestie, welcome to the std::ranges...sform_view,(3) page from the C++ Standard Libary manual 💖 — yes, that manual name is spelled exactly like that, and yes, we're keeping it.

✨ NAME ✨

bestie the page name is literally:

  • std::ranges::views::adjacent_transform,std::ranges::adjacent_transform_view,
  • and then the raw page repeats it: std::ranges::views::adjacent_transform,std::ranges::adjacent_transform_view,

there's also a little - line sitting between those repeats in the raw page. iconic formatting, no notes 💅

✨ Synopsis ✨

(1) is (since C++23) and it is giving class template energy:

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>>

(2) is also (since C++23):

namespace views {

template< std::size_t N >
inline constexpr /* unspecified */ adjacent_transform = /* unspecified */;

}

(3) is also (since C++23):

namespace views {

inline constexpr auto pairwise_transform = adjacent_transform<2>;

}

💅 Call signature 💅

and here's the call signature, (since C++23) bestie:

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

template< class F >
constexpr /*range adaptor closure*/ adjacent_transform<N>( F&& fun );
  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 the produced view is:

  • S - N + 1, if S >= N,
  • 0 otherwise, and the resulting view is empty.
  1. 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.
  2. 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 the adapted view type models the corresponding concept. periodt 🌈

🌸 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 n^th element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

🎀 Deduction guides 🎀

(none) — not a single one, bestie. truly minimal 💀

🦋 Member types 🦋

  • 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 🍓

  • fun_ (private) — /*movable-box*/<F> (exposition-only member object*)
  • inner_ (private) — ranges::adjacent_view<V,N> (exposition-only member object*)

🧚 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 girlies, assemble:

  • __cpp_lib_ranges_zip — value 202110L — Std (C++23) — Feature: std::ranges::zip_view, std::ranges::zip_transform_view, std::ranges::adjacent_view, std::ranges::adjacent_transform_view

🔥 Example 🔥

// Run this code

#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 💀

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)

source: http://cppreference.com · version/date: 2024.06.10 · page: std::ranges...sform_view,(3) 🫶✨

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