std::ranges::view, std::ranges::enable_view, std::ranges::view_base

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_reference_trange_rvalue_reference_t	range_value_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewistream_view
Adaptors
views::all_tviews::all common_viewviews::common filter_viewviews::filter reverse_viewviews::reverse	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform	join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split ref_view views::counted
Range adaptor objects
Range adaptor closure objects
Helper items
copyable-box	simple-view

 

Defined in header <ranges>
template<class T> concept view = ranges::range<T> && std::movable<T> && ranges::enable_view<T>;	(1)	(since C++20)
template<class T> inline constexpr bool enable_view =     std::derived_from<T, view_base> || /*is-derived-from-view-interface*/<T>;	(2)	(since C++20)
struct view_base { };	(3)	(since C++20)

1) The view concept specifies the requirements of a range type that has constant time copy, move, and assignment operations (e.g. a pair of iterators, or a generator Range that creates its elements on-demand. Notably, the standard library containers are ranges, but not views)

2) The enable_view variable template is used to indicate whether a range is a view. /*is-derived-from-view-interface*/<T> is true if and only if T has exactly one public base class ranges::view_interface<U> for some type U, and T has no base classes of type ranges::view_interface<V> for any other type V.
Users may specialize enable_view to true for cv-unqualified program-defined types which model view, and false for types which do not. Such specializations must be usable in constant expressions and have type const bool.

3) Deriving from view_base enables range types to model view.

Notes

By default, a type modeling movable and range is considered a view if it is publicly and unambiguously derived from view_base, or exactly one specialization of ranges::view_interface.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
P2325R3	C++20	view required default_initializable	does not require
LWG 3549	C++20	enable_view did not detect inheritance from view_interface	detects