std::ranges::View, std::ranges::enable_view, std::ranges::view_base
Defined in header <ranges>
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template<class T> concept View = Range<T> && Semiregular<T> && enable_view<T>; |
(1) | |
template<class T> inline constexpr bool enable_view = /*see description*/ ; |
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struct view_base { }; |
(3) | |
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 that whether a
Range
is a View, as follows:
For a type T, the default value of enable_view<T> is:
- If DerivedFrom<T, view_base> is true, enable_view<T> is true.
- Otherwise, if T is a specialization of class template std::initializer_list, std::set, std::multiset, std::unordered_set, std::unordered_multiset, std::match_results, enable_view<T> is false
- Otherwise, if both T and const T model
Range
and iter_reference_t<iterator_t<T>> is not the same type as iter_reference_t<iterator_t<const T>>, enable_view<T> is false. (in other words, deep constness implies element ownership, shallow constness implies reference (view) semantics) - Otherwise, enable_view<T> is true.
Notes
Users may derive from view_base or specialize enable_view to true for types which model View
, and specialize enable_view to false for types which do not.