std::ranges::views::as_rvalue, std::ranges::as_rvalue_view
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(exposition-only member object*)
returns the approximate size of the underlying
(public member function)
returns a constant iterator to the beginning of the range
(public member function of
returns a sentinel for the constant iterator of the range
(public member function of
casts the result of dereferencing an object to its associated rvalue reference type
(customization point object)[edit]
(C++23)(C++23)
(C++23)(C++23)
as_rvalue_viewviews::as_rvalue
(C++23)(C++23)
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
Defined in header
<ranges>
template< ranges::view V >
(1)
(since C++23)
requires ranges::input_range <V>
class as_rvalue_view
namespace views {
(2)
(since C++23)
inline constexpr /* unspecified */ as_rvalue = /* unspecified */;
Call signature
template< ranges::viewable_range R >
(since C++23)
requires /* see below */
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,
Tmodelsinput_range, and std::same_as <ranges::range_rvalue_reference_t <T>, ranges::range_reference_t <T>> is true; - as_rvalue_view{e} otherwise.
Contents
[edit] Data members
Member
Description
V base_ (private)
the underlying view(exposition-only member object*)
[edit] Member functions
(C++26)
approximately_sized_range (public member function)
Inherited from std::ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies
(public member function of
sized_range or forward_range (public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(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
(public member function of
std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies
(public member function of
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
(public member function of
bidirectional_range and common_range (public member function of
std::ranges::view_interface<D>) [edit]
returns the
(public member function of
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)
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)
requires ranges::approximately_sized_range<V>;
constexpr auto reserve_hint() const
requires ranges::approximately_sized_range<const V>;
(2)
(since C++26)
requires ranges::approximately_sized_range<const V>;
Returns ranges::reserve_hint(base_ ).
[edit] Deduction guides
template< class R >
as_rvalue_view( R&& ) -> as_rvalue_view<views::all_t <R>>;
(since C++23)
as_rvalue_view( R&& ) -> as_rvalue_view<views::all_t <R>>;
[edit] Helper templates
template< class T >
(since C++23)
constexpr bool enable_borrowed_range<std::ranges::as_rvalue_view<T>> =
This specialization of ranges::enable_borrowed_range makes as_rvalue_view satisfy borrowed_range when the underlying view satisfies it.
[edit] 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
|
[edit] 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"
[edit] 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 |
[edit] See also
(C++20)
(customization point object)[edit]