Defined in header <ranges> | ||
|---|---|---|
template< ranges::view V >
requires ranges::input_range<V>
class as_const_view
: public ranges::view_interface<as_const_view<V>>
| (1) | (since C++23) |
namespace views {
inline constexpr /* unspecified */ as_const = /* unspecified */;
}
| (2) | (since C++23) |
| Call signature | ||
template< ranges::viewable_range R >
requires /* see below */
constexpr ranges::view auto as_const( R&& r );
| (since C++23) |
view that is also a constant_range. An as_const_view always has read-only elements (if not empty).e be a subexpression, let T be decltype((e)), and let U be std::remove_cvref_t<T>. Then the expression views::as_const(e) is expression-equivalent to: views::all(e), if it is a well-formed expression and views::all_t<T> models constant_range; std::span<const X, Extent>(e) for some type X and some extent Extent if U denotes std::span<X, Extent>; ranges::ref_view(static_cast<const X&>(e.base())) if U denotes ranges::ref_view<X> for some type X and const X models constant_range; ranges::ref_view(static_cast<const U&>(e)) if e is an lvalue, const U models constant_range, and U does not model view. as_const_view{e}.as_const_view always models constant_range, and it models the contiguous_range, random_access_range, bidirectional_range, forward_range, borrowed_range, common_range, and sized_range when the underlying view V models respective concepts.
Typical implementations of as_const_view only hold one non-static data member:
V (shown here as base_, the name is exposition only). |
(C++23) | constructs an as_const_view (public member function) |
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(C++23) | returns the underlying view V (public member function) |
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(C++23) | returns the beginning iterator of the as_const_view (public member function) |
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(C++23) | returns the end iterator of the as_const_view (public member function) |
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(C++23) | returns the size of the view if it is bounded (public member function) |
Inherited from |
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(C++20) | returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function of std::ranges::view_interface<D>) |
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(C++23) | 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) | returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) |
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(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>) |
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(C++20) | gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function of std::ranges::view_interface<D>) |
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(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>) |
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(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>) |
as_const_view() requires std::default_initializable<V> = default; | (1) | (since C++23) |
constexpr explicit as_const_view( V base ); | (2) | (since C++23) |
base_ via its default member initializer (= V()).base_ with std::move(base).| base | - | a view |
constexpr V base() const& requires std::copy_constructible<V>; | (1) | (since C++23) |
constexpr V base() &&; | (2) | (since C++23) |
Returns the underlying view.
return base_;.return std::move(base_);. constexpr auto begin() requires (!__simple_view<V>); | (1) | (since C++23) |
constexpr auto begin() const requires ranges::range<const V>; | (2) | (since C++23) |
Returns the constant iterator of the view.
return ranges::cbegin(base_);
constexpr auto end() requires (!__simple_view<V>); | (1) | (since C++23) |
constexpr auto end() const requires ranges::range<const V>; | (2) | (since C++23) |
Returns the constant sentinel of the view.
return ranges::cend(base_);
constexpr auto size() requires ranges::sized_range<V>; | (1) | (since C++23) |
constexpr auto size() const requires ranges::sized_range<const V>; | (2) | (since C++23) |
Returns the size of the view if the view is bounded.
return ranges::size(base_);
template< class R > as_const_view( R&& ) -> as_const_view<views::all_t<R>>; | (since C++23) |
template< class T >
inline constexpr bool enable_borrowed_range<std::ranges::as_const_view<T>> =
std::ranges::enable_borrowed_range<T>;
| (since C++23) |
This specialization of std::ranges::enable_borrowed_range makes as_const_view satisfy borrowed_range when the underlying view satisfies it.
| Feature-test macro | Value | Std | Comment |
|---|---|---|---|
__cpp_lib_ranges_as_const | 202207L | (C++23) |
std::ranges::as_const_view, std::const_iterator |
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(C++23) | a view of a sequence that casts each element to an rvalue (class template) (range adaptor object) |
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(C++20) | returns an iterator to the beginning of a read-only range (customization point object) |
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(C++20) | returns a sentinel indicating the end of a read-only range (customization point object) |
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(C++17) | obtains a reference to const to its argument (function template) |
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