std::ranges::views::as_const, std::ranges::as_const_view

< cpp‎ | ranges
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)
1) A range adaptor that represents a view of underlying view that is also a constant_range. An as_const_view always has read-only elements (if not empty).
2) RangeAdaptorObject. Let 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:

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

Typical implementations of as_const_view hold only one non-static data member:

  • base_ (exposition only*) - The underlying view of type V.

Member functions

(C++23)
 constructs an as_const_view
(public member function)
(C++23)
 returns the underlying view V
(public member function)
(C++23)
 returns the beginning iterator of the as_const_view
(public member function)
(C++23)
 returns the end iterator of the as_const_view
(public member function)
(C++23)
 returns the size of the view if it is bounded
(public member function)
Inherited from std::ranges::view_interface
(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>)
(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>)
(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>)
(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>)
(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>)
(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>)
(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>)

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)
1) Value-initializes base_ via its default member initializer (= V()).
2) Initializes 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.

1) Copy-constructs the result from the underlying view. Equivalent to return base_;.
2) Move-constructs the result from the underlying view. Equivalent to return std::move(base_);.

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.

1,2) Equivalent to return ranges::cbegin(base_);

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.

1,2) Equivalent to return ranges::cend(base_);

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.

1,2) Equivalent to return ranges::size(base_);

Deduction guides

template< class R >
as_const_view( R&& ) -> as_const_view<views::all_t<R>>;
 (since C++23)

Helper templates

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.

Notes

Feature-test macro Value Std Comment
__cpp_lib_ranges_as_const 202207L (C++23) std::ranges::as_const_view, std::const_iterator

Example

This section is incomplete
Reason: example

See also

(C++23)
 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)