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std::ranges::owning_view

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)

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.

Data members

Member name Definition
r_ (private) The underlying range of type R.
(exposition-only member object*)

Member functions

(C++20)
constructs an owning_view by value-initializing or move-constructing the stored range
(public member function)
(C++20)
move-assigns the stored range
(public member function)
(C++20)
returns a reference to the stored range
(public member function)
(C++20)
returns the beginning iterator of the stored range
(public member function)
(C++20)
returns the sentinel of the stored range
(public member function)
(C++20)
checks whether the stored range is empty
(public member function)
(C++20)
returns the size of the stored sized_range
(public member function)
(C++20)
returns the pointer to the beginning of the stored contiguous_range
(public member function)
Inherited from std::ranges::view_interface
(C++23)
returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D>)
(C++23)
returns a sentinel for the constant iterator of the range.
(public member function of std::ranges::view_interface<D>)
(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>)
(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>)
(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>)
(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>)

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

#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

(C++20)
a view of the elements of some other range
(class template)
(C++20)
a view that includes all elements of a range
(alias template) (range adaptor object)

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