std::ranges::owning_view(3)

💖 std::ranges::owning_view 💖

Okay so this is the std::ranges::owning_view(3) page from the C++ Standard Libary manual (yes, that spelling is literally in the header bestie 💀). It’s giving “I own this range, I do not share it” energy, and honestly? Iconic. 💅

🌸 NAME 🌸

std::ranges::owning_view — std::ranges::owning_view

✨ Synopsis ✨

Defined in header <ranges>.

template< ranges::range R >
    requires std::movable<R> && (!/*is-initializer-list*/<R>)
class owning_view
    : public ranges::view_interface<owning_view<R>>

(since C++20) — yup, this whole vibe is C++20 coded.

owning_view is a view that has unique ownership of a range. It is move-only and stores that range within it.

The constant /*is-initializer-list*/<R> in the requires-clause is true if and only if std::remove_cvref_t<R> is a specialization of std::initializer_list.

🧚 Member functions 🧚

• constructor (C++20) — constructs an owning_view by value-initializing or move-constructing the stored range (public member function).
• operator= (C++20) — move-assigns the stored range (public member function).
• base (C++20) — returns a reference to the stored range (public member function).
• begin (C++20) — returns the beginning iterator of the stored range (public member function).
• end (C++20) — returns the sentinel of the stored range (public member function).
• empty (C++20) — checks whether the stored range is empty (public member function).
• size (C++20) — returns the size of the stored sized_range (public member function).
• data (C++20) — returns the pointer to the beginning of the stored contiguous_range (public member function).

🌈 Inherited from std::ranges::view_interface

• 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>)

💅 std::ranges::owning_view::owning_view

owning_view() requires std::default_initializable<R> = default; (1) (since C++20)
owning_view( owning_view&& other ) = default;                   (2) (since C++20)
constexpr owning_view( R&& t );                                 (3) (since C++20)
owning_view( const owning_view& ) = delete;                     (4) (since C++20)

1. Default constructor. Value-initializes the stored range by its default member initializer (= R()).
2. Move constructor. Move constructs the stored range from that of other.
3. Move constructs the stored range from t.
4. Copy constructor is deleted. owning_view is move-only.

Parameters

• other — another owning_view to move from
• t — range to move from

💜 std::ranges::owning_view::operator=

owning_view& operator=( owning_view&& other ) = default; (1) (since C++20)
owning_view& operator=( const owning_view& ) = delete;   (2) (since C++20)

1. Move assignment operator. Move assigns the stored range from that of other.
2. Copy assignment operator is deleted. owning_view is move-only.

Parameters

• other — another owning_view to move from

Return value

*this

🦋 std::ranges::owning_view::base

constexpr R& base() & noexcept;               (1) (since C++20)
constexpr const R& base() const & noexcept;   (2) (since C++20)
constexpr R&& base() && noexcept;             (3) (since C++20)
constexpr const R&& base() const && noexcept; (4) (since C++20)

Returns a reference to the stored range, keeping value category and const-qualification.

• 1,2) Equivalent to return r_;.
• 3,4) Equivalent to return std::move(r_);.

🌸 std::ranges::owning_view::begin

constexpr ranges::iterator_t<R> begin();                      (1) (since C++20)
constexpr auto begin() const requires ranges::range<const R>; (2) (since C++20)

Equivalent to return ranges::begin(r_);.

🎀 std::ranges::owning_view::end

constexpr ranges::sentinel_t<R> end();                      (1) (since C++20)
constexpr auto end() const requires ranges::range<const R>; (2) (since C++20)

Equivalent to return ranges::end(r_);.

🌟 std::ranges::owning_view::empty

constexpr bool empty() requires requires { ranges::empty(r_); };       (1) (since C++20)
constexpr bool empty() const requires requires { ranges::empty(r_); }; (2) (since C++20)

Equivalent to return ranges::empty(r_);.

🍓 std::ranges::owning_view::size

constexpr auto size() requires ranges::sized_range<R>;             (1) (since C++20)
constexpr auto size() const requires ranges::sized_range<const R>; (2) (since C++20)

Equivalent to return ranges::size(r_);.

👑 std::ranges::owning_view::data

constexpr auto data() requires ranges::contiguous_range<R>;             (1) (since C++20)
constexpr auto data() const requires ranges::contiguous_range<const R>; (2) (since C++20)

Equivalent to return ranges::data(r_);.

🧚 Helper templates

template< class T >
inline constexpr bool
enable_borrowed_range<std::ranges::owning_view<T>> =
    std::ranges::enable_borrowed_range<T>;

(since C++20)

This specialization of std::ranges::enable_borrowed_range makes owning_view satisfy borrowed_range when the underlying range satisfies it.

🔥 Example 🔥

// Run this code

#include <cassert>
#include <iostream>
#include <ranges>
#include <string>

int main()
{
    using namespace std::literals;
    std::ranges::owning_view ov{"cosmos"s}; // the deduced type of R is std::string;
                                            // `ov` is the only owner of this string
    assert(
        ov.empty() == false &&
        ov.size() == 6 &&
        ov.size() == ov.base().size() &&
        ov.front() == 'c' &&
        ov.front() == *ov.begin() &&
        ov.back() == 's' &&
        ov.back() == *(ov.end() - 1) &&
        ov.data() == ov.base()
    );

    std::cout << "sizeof(ov): " << sizeof ov << '\n' // typically equal to sizeof(R)
              << "range-for: ";
    for (const char ch : ov)
        std::cout << ch;
    std::cout << '\n';

    std::ranges::owning_view<std::string> ov2;
    assert(ov2.empty());
//  ov2 = ov; // compile-time error: copy assignment operator is deleted
    ov2 = std::move(ov); // OK
    assert(ov2.size() == 6);
}

🌈 Possible output 🌈

sizeof(ov): 32
range-for: cosmos

💖 See also 💖

• ranges::ref_view — a view of the elements of some other range (C++20) (class template)
• views::all_t, views::all — a view that includes all elements of a range (C++20); views::all_t is the alias template and views::all is the range adaptor object.

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Okay bestie, that’s the whole page 🫶 Source: http://cppreference.com. Version/date: 2024.06.10. Page: std::ranges::owning_view(3). Now go own a range and slay 💅✨