std::ranges...::chunk_view(3)

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

💖 NAME

okay bestie, this is the std::ranges...::chunk_view(3) page from the C++ Standard Libary — manual name secured, let's go. 💅

std::ranges::views::chunk,std::ranges::chunk_view — std::ranges::views::chunk,std::ranges::chunk_view

✨ SYNOPSIS

Defined in header <ranges>
template< ranges::view V >

    requires ranges::input_range<V>                           (1)
(since C++23)
class chunk_view

    : public ranges::view_interface<chunk_view<V>>
template< ranges::view V >

    requires ranges::forward_range<V>                         (2)
(since C++23)
class chunk_view<V>

    : public ranges::view_interface<chunk_view<V>>
namespace views {

    inline constexpr /* unspecified */ chunk = /* unspecified (3)
(since C++23)
*/;

}
Call signature
template< ranges::viewable_range R >
constexpr ranges::view auto chunk( R&& r,
(since C++23)
ranges::range_difference_t<R> n );
template< class DifferenceType >
constexpr /*range adaptor closure*/ chunk( DifferenceType&& n
(since C++23)
);
Helper templates
template< class I >                                           (4)
(exposition only*)
constexpr I __div_ceil( I num, I denom );

okay so chunk_view takes a view and a number n, and it serves you a range of views — the chunks — of the original view. Every chunk except maybe the last one has size n. These chunks are non-overlapping, successive sub-ranges of the elements of the original view, in order. no cap. 🫶

Let s be the size of the original view. If s is not a multiple of n, the size of the last produced view is exactly s % n (the remainder). Otherwise, the size of each chunk, including the last one, is n.

The size of the produced view is __div_ceil(s).

If n is not greater than 0, the behavior is undefined. bestie, do not do that. literally undefined behavior is not a vibe. 💀
  1. An implementation that supports the underlying view V that models only input_range.
  2. A partial specialization that supports the underlying view V that models forward_range or stronger. Models common_range if the underlying view V is forward_range, common_range, and either sized_range or non bidirectional_range.
  3. The name views::chunk denotes a RangeAdaptorObject. Given subexpressions e and n, the expression views::chunk(e, n) is expression-equivalent to chunk_view(e, n).
  4. Computes the smallest integer value that is not less than the quotient of dividing num by denom. Equivalent to:
I r = num / denom;
if (num % denom)
    ++r;
return r;

🫶 MEMBER FUNCTIONS

  • constructor — constructs a chunk_view. (C++23) (public member function)
  • base — returns a copy of the underlying (adapted) 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

this page literally just drops the heading and moves on — no deduction guides listed here. iconic minimalism, i guess. 🎀

🦋 NESTED CLASSES

  • outer_iterator — the output ("chunk-wise") iterator type when V models input_range (1). (C++23) (exposition-only member class*)
  • inner_iterator — the inner ("element-wise") iterator type when V models input_range (1). (C++23) (exposition-only member class*)
  • iterator — the iterator type when V models forward_range (2). (C++23) (exposition-only member class template*)

🌸 HELPER TEMPLATES

template< class V >

inline constexpr bool ranges::enable_borrowed_range<chunk_view<V>> =
(since C++23)

    ranges::forward_range<V> && ranges::enable_borrowed_range<V>;

This specialization of ranges::enable_borrowed_range makes chunk_view satisfy borrowed_range when the underlying view V satisfies both, the forward_range and the borrowed_range. 🫶

📝 NOTES

  • If V models input_range (1), chunk_view's iterator has a dedicated type: outer_iterator::value_type that is itself an input view.
  • If V models forward_range or stronger (2), chunk_view defers to views::take for its value_type.
  • If V models bidirectional_range or stronger ranges (2), the need to calculate size the last chunk correctly (from the end iterator) requires the underlying range type V to be sized_range.

Feature-test macro:

  • __cpp_lib_ranges_chunk — value 202202L, std (C++23), feature std::ranges::chunk_view.

💻 EXAMPLE

// Run this code

#include <algorithm>
#include <iostream>
#include <ranges>

auto print_subrange = [](std::ranges::viewable_range auto&& r)
{
    std::cout << '[';
    for (int pos{}; auto elem : r)
        std::cout << (pos++ ? " " : "") << elem;
    std::cout << "] ";
};

int main()
{
    const auto v = {1, 2, 3, 4, 5, 6};

    for (const unsigned width : std::views::iota(1U, 2U + v.size()))
    {
        auto const chunks = v | std::views::chunk(width);
        std::cout << "chunk(" << width << "): ";
        std::ranges::for_each(chunks, print_subrange);
        std::cout << '\n';
    }
}

🔥 OUTPUT

chunk(1): [1] [2] [3] [4] [5] [6]
chunk(2): [1 2] [3 4] [5 6]
chunk(3): [1 2 3] [4 5 6]
chunk(4): [1 2 3 4] [5 6]
chunk(5): [1 2 3 4 5] [6]
chunk(6): [1 2 3 4 5 6]
chunk(7): [1 2 3 4 5 6]

📚 REFERENCES

  • C++23 standard (ISO/IEC 14882:2023):
  • 26.7.28 Chunk view [range.chunk]

👀 SEE ALSO

  • ranges::chunk_by_view / views::chunk_by — splits the view into subranges between each pair of adjacent elements for which the given predicate returns false. (C++23) (class template) (range adaptor object)
  • ranges::adjacent_view / views::adjacent — a view consisting of tuples of references 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)

okay that's the whole page, bestie — source/version vibes: http://cppreference.com, dated 2024.06.10, for std::ranges...::chunk_view(3). bye 💖

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