std::ranges::ref_view
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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 referenced
(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
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++26)(C++26)
ref_view
(C++23)(C++23)
(C++26)(C++26)
(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::range R >
(since C++20)
requires std::is_object_v <R>
class ref_view
ref_view is a view of the elements of some other range. It wraps a reference to that range.
Contents
[edit] Data members
Member
Description
R* r_
a pointer to the underlying range(exposition-only member object*)
[edit] Member functions
(C++26)
approximately_sized_range (public member function)
Inherited from std::ranges::view_interface
(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::ref_view::ref_view
template< /*different-from*/<ref_view> T >
(since C++20)
requires std::convertible_to <T, R&> &&
requires { _FUN(std::declval <T>()); }
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)
requires requires { ranges::empty (*r_); };
Returns ranges::empty (*r_ ).
std::ranges::ref_view::size
constexpr auto size() const
requires ranges::sized_range <R>;
(since C++20)
requires ranges::sized_range <R>;
Returns ranges::size (*r_ ).
std::ranges::ref_view::reserve_hint
constexpr auto size() const
requires ranges::approximately_sized_range<R>;
(since C++26)
requires ranges::approximately_sized_range<R>;
Returns ranges::reserve_hint(*r_ ).
std::ranges::ref_view::data
constexpr auto data() const
requires ranges::contiguous_range <R>;
(since C++20)
requires ranges::contiguous_range <R>;
Returns ranges::data (*r_ ).
[edit] Deduction guides
template< class R >
ref_view( R& ) -> ref_view<R>;
(since C++20)
ref_view( R& ) -> ref_view<R>;
[edit] Helper templates
template< class T >
constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true;
(since C++20)
constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true;
This specialization of std::ranges::enable_borrowed_range makes ref_view satisfy borrowed_range.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_reserve_hint |
202502L |
(C++26) | ranges::approximately_sized_range and reserve_hint
|
[edit] Example
Run this code
#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
[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 |
|---|---|---|---|
| P2325R3 | C++20 | default constructor was provided asview must be default_initializable
|
removed along with the requirement |