std::ranges::owning_view

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_trange_value_trange_reference_t	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)	elements_of (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Range factories
empty_viewviews::empty single_viewviews::single	iota_viewviews::iota repeat_viewviews::repeat (C++23)(C++23)	basic_istream_viewviews::istream
Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23) filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23) lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)
Range generators
std::generator (C++23)
Range adaptor objects
Range adaptor closure objects
range_adaptor_closure (C++23)
Helper items
copyable-box movable-box (until C++23)(C++23)	simple-view non-propagating-cache

 

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

Typical implementations of owning_view have only one non-static data member: the underlying range of type R. The member is shown as r_ here (the name is exposition-only).

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 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

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 and
        ov.size() == 6 and
        ov.size() == ov.base().size() and
        ov.front() == 'c' and
        ov.front() == *ov.begin() and
        ov.back() == 's' and
        ov.back() == *(ov.end() - 1) and
        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 (C++20)	a view of the elements of some other range (class template)
views::all_tviews::all (C++20)	a view that includes all elements of a range (alias template) (range adaptor object)