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std::ranges::views::as_rvalue, std::ranges::as_rvalue_view - cppreference.com

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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

constructs an as_rvalue_view
(public member function)
returns the underlying view V
(public member function)
returns the beginning iterator of the as_rvalue_view
(public member function)
returns the end iterator of the as_rvalue_view
(public member function)
returns the size of the view if it is bounded
(public member function)
returns the approximate size of the underlying approximately_sized_range
(public member function)
Inherited from ranges::view_interface
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>) [edit]

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]
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>) [edit]
returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit]
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>) [edit]
returns the nth element in the derived view, provided only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit]

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

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

#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

See also