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std::ranges::views::as_input, std::ranges::as_input_view - cppreference.com

From cppreference.com

Defined in header <ranges> 

template< ranges::input_range V >
    requires ranges::view<V>
class as_input_view
    : public ranges::view_interface<as_input_view<V>>
(1) (since C++26) 
namespace views {
    inline constexpr /* unspecified */ as_input = /* unspecified */;
}
(2) (since C++26)

Call signature

 
template< ranges::viewable_range R >
    requires /* see below */
constexpr ranges::view auto as_input( R&& r );
(since C++26)

Consequently, as_input_view never models range concepts that are stronger than input_range. In particular, it does not model all of these:

Additionally, as_input_view does not model common_range. However, it does model borrowed_range, constant_range, and sized_range when the underlying view V models respective concepts.

Data members

Member Description
V base_ (private) the underlying view
(exposition-only member object*)

Member functions

constructs an as_input_view
(public member function)
returns a copy of the underlying (adapted) view
(public member function)
returns an iterator to the beginning
(public member function)
returns an iterator or a sentinel to the end
(public member function)
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range.
(public member function)
Inherited from ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit]
gets the address of derived view's data, provided only if its iterator type satisfies contiguous_iterator
(public member function of std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the last element in the derived view, provided only 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 only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit]

std::ranges::as_input_view::as_input_view

as_input_view() requires std::default_initializable<V> = default;
(1) (since C++26) 
constexpr explicit as_input_view( V base );
(2) (since C++26)

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

2) Initializes base_ with std::move(base).

Parameters

std::ranges::as_input_view::base

constexpr V base() const& requires std::copy_constructible<V>;
(1) (since C++26)
(2) (since C++26)

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_input_view::begin

constexpr auto begin() requires (!__simple_view<V>);
(1) (since C++26) 
constexpr auto begin() const requires ranges::range<const V>;
(2) (since C++26)

1) Equivalent to return /*iterator*/<false>(ranges::begin(base_));

2) Equivalent to return /*iterator*/<true>(ranges::begin(base_));

std::ranges::as_input_view::end

constexpr auto end() requires (!__simple_view<V>);
(1) (since C++26) 
constexpr auto end() const requires ranges::range<const V>;
(2) (since C++26)

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

std::ranges::as_input_view::size

constexpr auto size() requires ranges::sized_range<V>;
(1) (since C++26) 
constexpr auto size() const requires ranges::sized_range<const V>;
(2) (since C++26)

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

Deduction guides

template< class R >
as_input_view( R&& ) -> as_input_view<views::all_t<R>>;
(since C++26)

Nested classes

the iterator type
(exposition-only member class template*)

Helper templates

template< class T >
constexpr bool enable_borrowed_range<std::ranges::as_input_view<T>> =
    ranges::enable_borrowed_range<T>;
(since C++26)

This specialization of std::ranges::enable_borrowed_range makes as_input_view satisfy borrowed_range when the underlying view satisfies it.

Notes

as_input_view can be useful to avoid the overhead necessary to provide support for the operations needed for greater iterator strength.

Feature-test macro Value Std Feature
__cpp_lib_ranges_as_input 202502L (C++26) std::ranges::as_input_view

Example

See also