Defined in header <ranges> | ||
|---|---|---|
template< ranges::input_range V, std::size_t N >
requires ranges::view<V> &&
has-tuple-element<ranges::range_value_t<V>, N> &&
has-tuple-element<std::remove_reference_t<
ranges::range_reference_t<V>>, N> &&
returnable-element<ranges::range_reference_t<V>, N>
class elements_view : public ranges::view_interface<elements_view<V, N>>;
| (1) | (since C++20) |
namespace views {
template< std::size_t N >
inline constexpr /* unspecified */ elements = /* unspecified */;
}
| (2) | (since C++20) |
| Call signature | ||
template< ranges::viewable_range R >
requires /* see below */
constexpr ranges::view auto elements<N>( R&& r );
| (since C++20) | |
| Helper concepts | ||
| (3) | ||
template< class T, std::size_t N >
concept has-tuple-element = // exposition only
requires(T t) {
typename std::tuple_size<T>::type;
requires N < std::tuple_size_v<T>;
typename std::tuple_element_t<N, T>;
{ std::get<N>(t) } -> std::convertible_to<
const std::tuple_element_t<N, T>&>;
};
| (since C++20) (until C++23) | |
template< class T, std::size_t N >
concept has-tuple-element = // exposition only
tuple-like<T> && N < std::tuple_size_v<T>
| (since C++23) | |
template< class T, std::size_t N >
concept returnable-element = // exposition only
std::is_reference_v<T> || std::move_constructible<
std::tuple_element_t<N, T>>;
| (4) | (since C++20) |
view of tuple-like values, and issues a view with a value type of the N-th 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.tuple-like (since C++23).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.
|
(C++20) | constructs a elements_view (public member function) |
|
(C++20) | returns a copy of the underlying (adapted) view (public member function) |
|
(C++20) | returns an iterator to the beginning (public member function) |
|
(C++20) | returns an iterator or a sentinel to the end (public member function) |
|
(C++20) | returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (public member function) |
Inherited from |
|
|
(C++20) | 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>) |
|
(C++20) | 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>) |
|
(C++20) | returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | 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>) |
|
(C++20) | returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | the iterator type (exposition-only member class template) |
|
(C++20) | the sentinel type (exposition-only member class template) |
template<class T, std::size_t N>
inline constexpr bool enable_borrowed_range<std::ranges::elements_view<T, N>> =
std::ranges::enable_borrowed_range<T>;
| (since C++20) |
This specialization of std::ranges::enable_borrowed_range makes elements_view satisfy borrowed_range when the underlying view satisfies it.
#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
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 |
|
(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) |
|
(C++20) | 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) |
|
(C++23) | a view consisting of tuples 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) |
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