std::ranges:: views::as_rvalue, std::ranges::

Defined in header `<ranges>`
template < ranges::view V > requires ranges::input_range<V> class as_rvalue_view : public ranges::view_interface <as_rvalue_view<V>>	(1)	(since C++23)
namespace views { inline constexpr /* unspecified / as_rvalue = / unspecified */; }	(2)	(since C++23)
Call signature
template < ranges::viewable_range R > requires /* see below */ constexpr ranges::view auto as_rvalue( R&& r ) ;		(since C++23)

1) A range adaptor that represents a view of underlying view whose elements are rvalues.

2) RangeAdaptorObject. Let e be a subexpression and let T be decltype((e)). Then the expression views::as_rvalue(e) is expression-equivalent to:

views::all(e) , if it is a well-formed expression, T models input_range, and std::same_as < ranges::range_rvalue_reference_t <T>, ranges::range_reference_t <T>> is true
as_rvalue_view{e} otherwise.

Data members

Member object	Definition
`base_` (private)	The underlying view of type `V`. (exposition-only member object*

Member functions

(constructor)	constructs an `as_rvalue_view` (public member function)
base	returns the underlying view `V` (public member function)
begin	returns the beginning iterator of the `as_rvalue_view` (public member function)
end	returns the end iterator of the `as_rvalue_view` (public member function)
size	returns the size of the view if it is bounded (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`. (public member function of `std::ranges::view_interface<D>`)
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	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	returns the first element in the derived view. Provided if it satisfies `forward_range`. (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`. (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`. (public member function of `std::ranges::view_interface<D>`)

std::ranges::as_rvalue_view::as_rvalue_view

as_rvalue_view( ) requires std::default_initializable <V> = default ;	(1)	(since C++23)
constexpr explicit as_rvalue_view( V base );	(2)	(since C++23)

1) Value-initializes base_ via its default member initializer (= V()

2) Initializes base_ with std::move(base)

Parameters

base

-

a view

std::ranges::as_rvalue_view::base

constexpr V base( ) const & requires std::copy_constructible <V> ;	(1)	(since C++23)
constexpr V base() &&;	(2)	(since C++23)

Returns the underlying view.

1) Copy-constructs the result from the underlying view. Equivalent to return base_;

2) Move-constructs the result from the underlying view. Equivalent to return std::move(base_);

std::ranges::as_rvalue_view::begin

constexpr auto begin( ) requires ( ! /simple-view/ <V> ) ;	(1)	(since C++23)
constexpr auto begin( ) const requires ranges::range < const V> ;	(2)	(since C++23)

1,2) Returns std::move_iterator ( ranges::begin (base_) )

std::ranges::as_rvalue_view::end

constexpr auto end( ) requires ( ! /simple-view/ <V> ) ;	(1)	(since C++23)
constexpr auto end( ) const requires ranges::range < const V> ;	(2)	(since C++23)

1) Returns std::move_iterator ( ranges::end (base_) ) if V models common_range, otherwise std::move_sentinel ( ranges::end (base_) )

2) Returns std::move_iterator ( ranges::end (base_) ) if const V models common_range, otherwise std::move_sentinel ( ranges::end (base_) )

std::ranges::as_rvalue_view::size

constexpr auto size( ) requires ranges::sized_range <V> ;	(1)	(since C++23)
constexpr auto size( ) const requires ranges::sized_range < const V> ;	(2)	(since C++23)

Returns the size of the view if the view is bounded.

1,2) Equivalent to return ranges::size(base_);

Deduction guides

template < class R > as_rvalue_view( R&& ) - > as_rvalue_view< views::all_t <R>> ;		(since C++23)

Helper templates

template < class T > constexpr bool enable_borrowed_range<std:: ranges :: as_rvalue_view <T>> = ranges::enable_borrowed_range <T> ;		(since C++23)

This specialization of std::ranges::enable_borrowed_range makes as_rvalue_view satisfy borrowed_range

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_ranges_as_rvalue`	`202207L`	(C++23)	`std::ranges::as_rvalue_view`

Example

Run this code

#include <algorithm>
#include <iostream>
#include <ranges>
#include <string>
#include <vector>
 
int main()
{
    std::vector<std::string> words =
        {"the", "quick", "brown", "\N{FOX FACE}", "ate", "an", "archeopteryx"};
    std::vector<std::string> new_words;
 
    std::ranges::copy(
        words | std::views::as_rvalue,
        std::back_inserter(new_words)); // move string from words into new_words
 
    auto quoted = std::views::transform([](auto&& s) { return "“" + s + "”"; });
 
    std::cout << "Words: ";
    for (auto&& word : words | std::views::as_rvalue | quoted)
        std::cout << word << ' ';
 
    std::cout << "\nNew words: ";
    for (auto&& word : new_words | std::views::as_rvalue | quoted)
        std::cout << word << ' ';
}

Possible output:

Words: “” “” “” “” “” “” “” 
New words: “the” “quick” “brown” “🦊” “ate” “an” “archeopteryx”

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 4083	C++23	views::as_rvalue used to accept non-input ranges	made rejected

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External libraries

iter_move (C++20)	casts the result of dereferencing an object to its associated rvalue reference type (customization point object)
move_iterator (C++11)	iterator adaptor which dereferences to an rvalue (class template)
move_sentinel (C++20)	sentinel adaptor for std::move_iterator (class template)
ranges::as_const_viewviews::as_const (C++23)	converts a `view` into a `constant_range` (class template) (range adaptor object)