std::ranges::ref_view
Defined in header <ranges>
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||
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template
<
ranges::range R >
requires std::is_object_v<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 name | Definition |
r_ (private)
|
A pointer of type R* to the underlying range.(exposition-only member object* |
Member functions
constructs a ref_view that references to the given range (public member function) |
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| returns the references to the referenced range (public member function) |
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| returns the beginning iterator of the referenced range (public member function) |
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| returns the sentinel of the referenced range (public member function) |
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| checks whether the referenced range is empty (public member function) |
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returns the size of the referenced sized_range (public member function) |
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returns the pointer to the beginning of the referenced contiguous_range (public member function) |
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Inherited from std::ranges::view_interface |
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(C++23)
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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)
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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 if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
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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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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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returns the n
th element in the derived view. Provided 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
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template
<
/*different-from*/
<ref_view> T >
requires std::convertible_to
<T, R&
>
&& requires { _FUN(
std::declval
<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> ; |
(since C++20) | |
Equivalent to return ranges::size ( *r_) ;
std::ranges::ref_view::data
|
constexpr
auto data(
)
const
requires ranges::contiguous_range <R> ; |
(since C++20) | |
Equivalent to return ranges::data ( *r_) ;
Deduction guides
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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
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 as view
must 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) |