std::ranges::ref_view
Defined in header <ranges> |
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|---|---|---|
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
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).
Member functions
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(constructor)
(C++20)
|
constructs a ref_view that references to the given range (public member function) |
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base
(C++20)
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returns the references to the referenced range (public member function) |
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begin
(C++20)
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returns the beginning iterator of the referenced range (public member function) |
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end
(C++20)
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returns the sentinel of the referenced range (public member function) |
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empty
(C++20)
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checks whether the referenced range is empty (public member function) |
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size
(C++20)
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returns the size of the referenced sized_range (public member function) |
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data
(C++20)
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returns the pointer to the beginning of the referenced contiguous_range (public member function) |
Inherited from |
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(C++20)
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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>) |
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(C++20)
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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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(C++20)
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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)
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Returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) |
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::base
constexpr R& base() const; |
(since C++20) |
Equivalent to return *r_;
std::ranges::ref_view::begin
constexpr ranges::iterator_t<R> begin() const; |
(since C++20) |
Equivalent to return ranges::begin(*r_);
std::ranges::ref_view::end
constexpr ranges::sentinel_t<R> end() const; |
(since C++20) |
Equivalent to return ranges::end(*r_);
std::ranges::ref_view::empty
constexpr bool empty() const
requires requires { ranges::empty(*r_); }; |
(since C++20) |
Equivalent to return ranges::empty(*r_);
std::ranges::ref_view::size
constexpr auto size() const
requires ranges::sized_range<R>
{ return ranges::size(*r_); } |
(since C++20) |
std::ranges::ref_view::data
constexpr auto data() const
requires ranges::contiguous_range<R>
{ return ranges::data(*r_); } |
(since C++20) |
Deduction guides
template<class R> ref_view(R&) -> ref_view<R>; |
(since C++20) |
Helper templates
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.
Example
#include <ranges>
#include <iostream>
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 as viewmust be default_initializable |
removed along with the requirement |
See also
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(C++11)
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CopyConstructible and CopyAssignable reference wrapper (class template) |
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(C++20)
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a view with unique ownership of some range (class template) |
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(C++20)
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a view that includes all elements of a range (alias template) (range adaptor object) |
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