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

From cppreference.net

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

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	Description
`V` `base_` (private)	the underlying view ( 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)
reserve_hint (C++26)	returns the approximate size of the underlying `approximately_sized_range` (public member function)
Inherited from std::ranges::view_interface
empty	returns whether the derived view is empty, provided only 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 only 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 only 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 only 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)

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)

Returns std:: move_iterator ( ranges:: end ( base_ ) ) if (1) V or (2) const V models common_range .

Returns std:: move_sentinel ( ranges:: end ( base_ ) ) otherwise.

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

std::ranges::as_rvalue_view:: reserve_hint

constexpr auto reserve_hint ( ) requires ranges :: approximately_sized_range < V > ;	(1)	(since C++26)
constexpr auto reserve_hint ( ) const requires ranges :: approximately_sized_range < const V > ;	(2)	(since C++26)

Returns ranges :: reserve_hint ( 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 ranges::enable_borrowed_range makes as_rvalue_view satisfy borrowed_range when the underlying view satisfies it.

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_ranges_as_rvalue`	`202207L`	(C++23)	`std::ranges::as_rvalue_view`
`__cpp_lib_ranges_reserve_hint`	`202502L`	(C++26)	ranges::approximately_sized_range and `reserve_hint`

Example

Run this code

#include <algorithm>
#include <iostream>
#include <ranges>
#include <string>
#include <vector>
int main()
{
    std::vector<std::string> words =
        {"Quick", "red", "\N{FOX FACE}", "jumped", "over", "a", "pterodactyl"};
    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 << "Old 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:

Old words: “” “” “” “” “” “” “” 
New words: “Quick” “red” “🦊” “jumped” “over” “a” “pterodactyl”

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_view views::as_const (C++23)	converts a `view` into a `constant_range` (class template) (range adaptor object)

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