Difference between revisions of "cpp/ranges/ref view"
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Revision as of 08:13, 11 October 2021
| Defined in header <ranges>
|
||
| 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.
Contents |
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
| (constructor) (C++20) |
constructs a ref_view that references to the given range (public member function) |
| base (C++20) |
returns the references to the referenced range (public member function) |
| begin (C++20) |
returns the beginning iterator of the referenced range (public member function) |
| end (C++20) |
returns the sentinel of the referenced range (public member function) |
| empty (C++20) |
checks whether the referenced range is empty (public member function) |
| size (C++20) |
returns the size of the referenced sized_range (public member function) |
| data (C++20) |
returns the pointer to the beginning of the referenced contiguous_range (public member function) |
Inherited from std::ranges::view_interface | |
| (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>)
|
| 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>)
| |
returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
| |
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>)
| |
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>()); } |
(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) | |
std::ranges::ref_view::data
| constexpr auto data() const requires ranges::contiguous_range<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
| (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) |
