std::ranges...s::pairwise(3)

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

💖 std::ranges...s::pairwise(3) 💖

okay bestie, this page is from the C++ Standard Libary (yes, that spelling is literally right there), and it is lowkey giving “sliding windows but make it templates.” 💅

🌸 NAME 🌸

std::ranges::views::adjacent, std::ranges::adjacent_view, std::ranges::views::pairwise

-

std::ranges::views::adjacent, std::ranges::adjacent_view, std::ranges::views::pairwise

✨ Synopsis ✨

Defined in header <ranges>.

template< ranges::forward_range V, std::size_t N >
    requires ranges::view<V> && (N > 0)
class adjacent_view
    : public ranges::view_interface<adjacent_view<V, N>>

(1) (since C++23)

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

(2) (since C++23)

namespace views {
    inline constexpr auto pairwise = adjacent<2>;
}

(3) (since C++23)

📞 Call signature 📞

template< ranges::viewable_range R >
    requires /* see below */
constexpr ranges::view auto adjacent<N>( R&& r );

(since C++23)

1) adjacent_view is a range adaptor that takes a view, and produces a view whose i^th element (a “window”) is a std::tuple that holds N references to the elements of the original view, from i^th up to i + N - 1^th inclusively.

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<N> denotes a RangeAdaptorObject. Given a subexpression e and a constant expression N, the expression views::adjacent<N>(e) is expression-equivalent to

  • ((void)e, auto(views::empty<tuple<>>)) if N is equal to 0,
  • adjacent_view<views::all_t<decltype((e))>, N>(e) otherwise.

3) The name views::pairwise denotes a RangeAdaptorObject that behaves exactly as views::adjacent<2>.

adjacent_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 🎀

  • constructor — constructs a adjacent_view (C++23) (public member function)
  • begin — returns an iterator to the beginning (C++23) (public member function)
  • end — returns an iterator or a sentinel to the end (C++23) (public member function)
  • size — returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (C++23) (public member function)

🫶 Inherited from std::ranges::view_interface

  • empty — returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (C++20) (public member function of std::ranges::view_interface<D>)
  • cbegin — returns a constant iterator to the beginning of the range. (C++23) (public member function of std::ranges::view_interface<D>)
  • cend — returns a sentinel for the constant iterator of the range. (C++23) (public member function of std::ranges::view_interface<D>)
  • operator bool — returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (C++20) (public member function of std::ranges::view_interface<D>)
  • front — returns the first element in the derived view. Provided if it satisfies forward_range. (C++20) (public member function of std::ranges::view_interface<D>)
  • back — returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (C++20) (public member function of std::ranges::view_interface<D>)
  • operator[] — returns the n^th element in the derived view. Provided if it satisfies random_access_range. (C++20) (public member function of std::ranges::view_interface<D>)

🐚 Deduction guides 🐚

  • (none)

🦋 Nested classes 🦋

  • iterator — the iterator type. (C++23) (exposition-only member class template*)
  • sentinel — the sentinel type used when adjacent_view is not a common_range. (C++23) (exposition-only member class template*)

🌈 Helper templates 🌈

template< class V, size_t N >
inline constexpr bool ranges::enable_borrowed_range<adjacent_view<V, N>> =
    ranges::enable_borrowed_range<V>;

(since C++23)

This specialization of ranges::enable_borrowed_range makes adjacent_view satisfy borrowed_range when the underlying view satisfies it.

💀 Notes 💀

There are similarities between ranges::adjacent_view and ranges::slide_view:

  • Both create a “sliding window” of size N.
  • Both have the same size S - N + 1, where S is the size of an adapted view such that S >= N > 0.

The differences between these adapters are:

  • View adaptor: ranges::adjacent_view — value_type: A std::tuple object — The window size N: A template parameter
  • View adaptor: ranges::slide_view — value_type: A range — The window size N: A runtime parameter

Feature-test macro:

  • Feature-test macro: __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 <format>
#include <iostream>
#include <ranges>
#include <tuple>

int main()
{
    constexpr std::array v{1, 2, 3, 4, 5, 6};
    std::cout << "v = [1 2 3 4 5 6]\n";

    for (int i{}; std::tuple t : v | std::views::adjacent<3>)
    {
        auto [t0, t1, t2] = t;
        std::cout << std::format("e = {:<{}}[{} {} {}]\n", "", 2 * i++, t0, t1, t2);
    }
}

🌸 Output: 🌸

v = [1 2 3 4 5 6]
e = [1 2 3]
e =   [2 3 4]
e =     [3 4 5]
e =       [4 5 6]

👑 References 👑

  • C++23 standard (ISO/IEC 14882:2023):
    • 26.7.25 Adjacent view [range.adjacent]

🌟 See also 🌟

  • ranges::adjacent_transform_view / views::adjacent_transform — a view consisting of tuples of results of application of a transformation function to adjacent elements of the adapted view. (C++23) (class template) (range adaptor object)
  • ranges::slide_view / views::slide — a view whose M^th element is a view over the M^th through (M + N - 1)^th elements of another view. (C++23) (class template) (range adaptor object)
  • ranges::chunk_view / views::chunk — a range of views that are N-sized non-overlapping successive chunks of the elements of another view. (C++23) (class template) (range adaptor object)
  • ranges::stride_view / views::stride — a view consisting of elements of another view, advancing over N elements at a time. (C++23) (class template) (range adaptor object)

okay that is the whole page, bestie! source: http://cppreference.com, version/date: 2024.06.10, page: std::ranges...s::pairwise(3). slay 💖✨

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