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

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	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 returnstd::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) constV 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 returnranges::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

#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

ranges::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)

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

Data members

Member functions

Inherited from `std::ranges::view_interface`

std::ranges::as_rvalue_view::as_rvalue_view

Parameters

std::ranges::as_rvalue_view::base

std::ranges::as_rvalue_view::begin

std::ranges::as_rvalue_view::end

std::ranges::as_rvalue_view::size

std::ranges::as_rvalue_view::reserve_hint

Deduction guides

Helper templates

Notes

Example

Defect reports

See also

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

Data members

Member functions

Inherited from std::ranges::view_interface

std::ranges::as_rvalue_view::as_rvalue_view

Parameters

std::ranges::as_rvalue_view::base

std::ranges::as_rvalue_view::begin

std::ranges::as_rvalue_view::end

std::ranges::as_rvalue_view::size

std::ranges::as_rvalue_view::reserve_hint

Deduction guides

Helper templates

Notes

Example

Defect reports

See also

Inherited from `std::ranges::view_interface`