std::ranges::ref_view
Defined in header <ranges> | ||
|---|---|---|
template< ranges::range R >
requires std::is_object_v<R>
class ref_view
: public ranges::view_interface<ref_view<R>>
| (since C++20) |
ref_view is a view of the elements of some other range. It wraps a reference to that range.
Data members
| Member | Description |
|---|---|
R* r_ | a pointer to the underlying range (exposition-only member object*) |
Member functions
constructs a ref_view that references to the given range (public member function) |
|
| returns the references to the referenced range (public member function) |
|
| returns the beginning iterator of the referenced range (public member function) |
|
| returns the sentinel of the referenced range (public member function) |
|
| checks whether the referenced range is empty (public member function) |
|
returns the size of the referenced sized_range (public member function) |
|
|
(C++26) | returns the approximate size of the referenced approximately_sized_range (public member function) |
returns the pointer to the beginning of the referenced contiguous_range (public member function) |
|
Inherited from |
|
|
(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>) |
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(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>) |
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>) |
|
returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface<D>) |
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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>) |
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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>) |
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std::ranges::ref_view::ref_view
template< /*different-from*/<ref_view> T >
requires std::convertible_to<T, R&> &&
requires { _FUN(std::declval<T>()); }
constexpr ref_view( T&& t );
| (since C++20) |
Initializes r_ with std::addressof(static_cast<R&>(std::forward<T>(t))).
/*different-from*/<T, U> is satisfied if and only if std::remove_cvref_t<T> and std::remove_cvref_t<U> are not the same type, and overloads of _FUN are declared as void _FUN(R&); void _FUN(R&&) = delete;.
Parameters
| t | - | range to reference |
std::ranges::ref_view::begin
constexpr ranges::iterator_t<R> begin() const; | (since C++20) |
Returns ranges::begin(*r_ ).
std::ranges::ref_view::end
constexpr ranges::sentinel_t<R> end() const; | (since C++20) |
Returns ranges::end(*r_ ).
std::ranges::ref_view::empty
constexpr bool empty() const
requires requires { ranges::empty(*r_); };
| (since C++20) |
Returns ranges::empty(*r_ ).
std::ranges::ref_view::size
constexpr auto size() const
requires ranges::sized_range<R>;
| (since C++20) |
Returns ranges::size(*r_ ).
std::ranges::ref_view::reserve_hint
constexpr auto size() const
requires ranges::approximately_sized_range<R>;
| (since C++26) |
Returns ranges::reserve_hint(*r_ ).
std::ranges::ref_view::data
constexpr auto data() const
requires ranges::contiguous_range<R>;
| (since C++20) |
Returns ranges::data(*r_ ).
Deduction guides
template< class R > ref_view( R& ) -> ref_view<R>; | (since C++20) |
Helper templates
template< class T > constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true; | (since C++20) |
This specialization of std::ranges::enable_borrowed_range makes ref_view satisfy borrowed_range.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_reserve_hint | 202502L | (C++26) |
ranges::approximately_sized_range and reserve_hint |
Example
#include <iostream>
#include <ranges>
int main()
{
const std::string s{"cosmos"};
const std::ranges::take_view tv{s, 3};
const std::ranges::ref_view rv{tv};
std::cout
<< std::boolalpha
<< "call empty(): " << rv.empty() << '\n'
<< "call size() : " << rv.size() << '\n'
<< "call begin(): " << *rv.begin() << '\n'
<< "call end() : " << *(rv.end() - 1) << '\n'
<< "call data() : " << rv.data() << '\n'
<< "call base() : " << rv.base().size() << '\n' // ~> tv.size()
<< "range-for : ";
for (const auto c : rv)
std::cout << c;
std::cout << '\n';
}
Output:
call empty(): false call size() : 3 call begin(): c call end() : s call data() : cosmos call base() : 3 range-for : cos
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2325R3 | C++20 | default constructor was provided asview must be default_initializable | removed along with the requirement |
See also
|
(C++11) |
CopyConstructible and CopyAssignable reference wrapper (class template) |
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(C++20) | a view with unique ownership of some range (class template) |
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(C++20) | a view that includes all elements of a range(alias template) (range adaptor object) |
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