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

< cpp‎ | ranges
Defined in header <ranges>
template<class T>

concept view = ranges::range<T> && std::movable<T> &&

               std::default_initializable<T> && ranges::enable_view<T>;
template<class T>
inline constexpr bool enable_view = std::derived_from<T, view_base>;
struct view_base { };
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. By default, a type is considered a view if it is publicly and unambiguously derived from view_base.
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.