std::ranges::views::elements, std::ranges::elements_view
| Defined in header <ranges>
|
||
| template< ranges::input_range V, std::size_t N > requires ranges::view<V> && |
(1) | (since C++20) |
| namespace views { template< std::size_t N > |
(2) | (since C++20) |
| Call signature |
||
| template< ranges::viewable_range R > requires /* see below */ |
(since C++20) | |
| Helper concepts |
||
| (3) | ||
template< class T, std::size_t N > concept /*has-tuple-element*/ = |
(until C++23) (exposition only*) |
|
| template< class T, std::size_t N > concept /*has-tuple-element*/ = |
(since C++23) (exposition only*) |
|
| template< class T, std::size_t N > concept returnable-element = |
(4) | (exposition only*) |
view of tuple-like values, and issues a view with a value type of the Nth element of the adapted view's value-type.views::elements is a RangeAdaptorObject. The expression views::elements<M>(e) is expression-equivalent to elements_view<views::all_t<decltype((e))>, M>{e} for any suitable subexpression e and constant expression M.elements_view models the concepts random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying view V models respective concepts.
Data members
| Member name | Definition |
base_ (private)
|
the underlying (adapted) view of type V(exposition-only member object*) |
Member functions
constructs a elements_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 std::ranges::view_interface | |
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>) | |
| (C++23) |
returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>) |
| (C++23) |
returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) |
| 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>) | |
returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>) | |
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>) | |
returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) | |
Nested classes
| the iterator type (exposition-only member class template*) | |
| the sentinel type (exposition-only member class template*) |
Helper templates
| template<class T, std::size_t N> constexpr bool enable_borrowed_range<std::ranges::elements_view<T, N>> = |
(since C++20) | |
This specialization of ranges::enable_borrowed_range makes elements_view satisfy borrowed_range when the underlying view satisfies it.
Example
#include <iostream> #include <ranges> #include <string> #include <tuple> #include <vector> int main() { const std::vector<std::tuple<int, char, std::string>> vt { {1, 'A', "α"}, {2, 'B', "β"}, {3, 'C', "γ"}, {4, 'D', "δ"}, {5, 'E', "ε"}, }; for (int const e : std::views::elements<0>(vt)) std::cout << e << ' '; std::cout << '\n'; for (char const e : vt | std::views::elements<1>) std::cout << e << ' '; std::cout << '\n'; for (std::string const& e : std::views::elements<2>(vt)) std::cout << e << ' '; std::cout << '\n'; }
Output:
1 2 3 4 5 A B C D E α β γ δ ε
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3494 | C++20 | elements_view was never a borrowed_range
|
it is a borrowed_rangeif its underlying view is |
| LWG 3502 | C++20 | dangling reference could be obtained from elements_view
|
such usage is forbidden |
See also
| (C++20) |
takes a view consisting of pair-like values and produces a view of the first elements of each pair(class template) (range adaptor object) |
takes a view consisting of pair-like values and produces a view of the second elements of each pair(class template) (range adaptor object) | |
| (C++23) |
a view consisting of tuples of references to corresponding elements of the adapted views(class template) (customization point object) |
a view consisting of results of application of a transformation function to corresponding elements of the adapted views(class template) (customization point object) | |
| BLAS-like slice of a valarray: starting index, length, stride (class) |