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.
ref_view behaves as if it only stores a R* member subobject pointing to the referenced range. The member is shown as r_ here (the name is exposition-only).
|
(C++20) | constructs a ref_view that references to the given range (public member function) |
|
(C++20) | returns the references to the referenced range (public member function) |
|
(C++20) | returns the beginning iterator of the referenced range (public member function) |
|
(C++20) | returns the sentinel of the referenced range (public member function) |
|
(C++20) | checks whether the referenced range is empty (public member function) |
|
(C++20) | returns the size of the referenced sized_range (public member function) |
|
(C++20) | 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>) |
|
(C++23) | returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>) |
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(C++20) | returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) |
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;.
| t | - | range to reference |
constexpr R& base() const; | (since C++20) |
Equivalent to return *r_;
constexpr ranges::iterator_t<R> begin() const; | (since C++20) |
Equivalent to return ranges::begin(*r_);
constexpr ranges::sentinel_t<R> end() const; | (since C++20) |
Equivalent to return ranges::end(*r_);
constexpr bool empty() const
requires requires { ranges::empty(*r_); };
| (since C++20) |
Equivalent to return ranges::empty(*r_);
constexpr auto size() const
requires ranges::sized_range<R>;
| (since C++20) |
Equivalent to return ranges::size(*r_);
constexpr auto data() const
requires ranges::contiguous_range<R>;
| (since C++20) |
Equivalent to return ranges::data(*r_);
template< class R > ref_view( R& ) -> ref_view<R>; | (since C++20) |
template< class T > inline 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.
#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
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 as viewmust be default_initializable | removed along with the requirement |
|
(C++11) | CopyConstructible and CopyAssignable reference wrapper (class template) |
|
(C++20) | a view with unique ownership of some range (class template) |
|
(C++20) | a view that includes all elements of a range (alias template) (range adaptor object) |
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