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

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< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives



Dangling iterator handling
Range concepts
Views

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Adaptors
Range adaptor objects
Range adaptor closure objects
Helper items
 
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) Range adaptor object. 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.

Contents

[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if

  • e and f have the same effects, and
  • either both are constant subexpressions or else neither is a constant subexpression, and
  • either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

[edit] Data members

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

  • the underlying view of type V (shown here as base_, the name is exposition only).

[edit] Member functions

(constructor)
(C++23)
constructs an as_const_view
(public member function)
base
(C++23)
returns the underlying view V
(public member function)
begin
(C++23)
returns the beginning iterator of the as_const_view
(public member function)
end
(C++23)
returns the end iterator of the as_const_view
(public member function)
size
(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>) [edit]
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>) [edit]
(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>) [edit]
(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>) [edit]
(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>) [edit]
Returns the nth element in the derived view. Provided if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>) [edit]

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>) {

  return ranges::cbegin(base_);

}
(1) (since C++23)
constexpr auto begin() const requires ranges::range<const V> {

  return ranges::cbegin(base_);

}
(2) (since C++23)

Returns the constant iterator of the view.

std::ranges::as_const_view::end

constexpr auto end() requires (!/*simple-view*/<V>) {

  return ranges::cend(base_);

}
(1) (since C++23)
constexpr auto end() const requires ranges::range<const V> {

  return ranges::cend(base_);

}
(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> {

    return ranges::size(base_);

}
(1) (since C++23)
constexpr auto size() const requires ranges::sized_range<const V> {

    return ranges::size(base_);

}
(2) (since C++23)

Returns the size of the view if the view is bounded.

[edit] Deduction guides

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

[edit] 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.

[edit] Example

[edit] See also

returns an iterator to the beginning of a read-only range
(customization point object) [edit]
returns a sentinel indicating the end of a read-only range
(customization point object) [edit]