std::ranges::views::as_const, std::ranges::as_const_view
| Defined in header <ranges>
|
||
| template< ranges::view V > requires ranges::input_range<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 */ |
(since C++23) | |
view that is also a constant_range. An as_const_view always has read-only elements (if not empty).- views::all(e), if it is a well-formed expression and views::all_t<T> models
constant_range; - otherwise, std::span<const X, Extent>(e) for some type
Xand some extentExtentifUdenotes std::span<X, Extent>; - otherwise, ranges::ref_view(static_cast<const X&>(e.base())) if
Udenotes ranges::ref_view<X> for some typeXand const X modelsconstant_range; - otherwise, ranges::ref_view(static_cast<const U&>(e)) if
eis an lvalue, const U modelsconstant_range, andUdoes not modelview. - otherwise, 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.
Data members
| Member object | Definition |
base_ (private)
|
The underlying view of type V.(exposition-only member object*) |
Member functions
constructs an as_const_view (public member function) | |
returns the underlying view V (public member function) | |
returns the beginning iterator of the as_const_view (public member function) | |
returns the end iterator of the as_const_view (public member function) | |
| returns the size of the view if it is bounded (public member function) | |
Inherited from std::ranges::view_interface | |
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>) | |
| (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>) | |
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>) | |
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::as_const_view::as_const_view
| 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).Parameters
| base | - | a view |
std::ranges::as_const_view::base
| constexpr V base() const& requires std::copy_constructible<V>; |
(1) | (since C++23) |
| constexpr V base() &&; |
(2) | (since C++23) |
Returns the underlying view.
std::ranges::as_const_view::begin
| 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.
std::ranges::as_const_view::end
| 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.
std::ranges::as_const_view::size
| 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.
Deduction guides
| template< class R > as_const_view( R&& ) -> as_const_view<views::all_t<R>>; |
(since C++23) | |
Helper templates
| template< class T > constexpr bool enable_borrowed_range<std::ranges::as_const_view<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.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_as_const |
202207L |
(C++23) | ranges::as_const_view, std::const_iterator
|
Example
#include <cassert> #include <ranges> int main() { int x[]{1, 2, 3, 4, 5}; auto v1 = x | std::views::drop(2); assert(v1.back() == 5); v1[0]++; // OK, can modify non-const element auto v2 = x | std::views::drop(2) | std::views::as_const; assert(v2.back() == 5); // v2[0]++; // Compile-time error, cannot modify read-only element }
See also
a view of a sequence that casts each element to an rvalue(class template) (range adaptor object) | |
| (C++20) |
returns an iterator to the beginning of a read-only range (customization point object) |
| (C++20) |
returns a sentinel indicating the end of a read-only range (customization point object) |
| (C++17) |
obtains a reference to const to its argument (function template) |
| (C++23) |
iterator adaptor that converts an iterator into a constant iterator (class template) |