Defined in header <ranges> | ||
|---|---|---|
template< ranges::input_range V >
requires ranges::view<V> and
ranges::input_range<ranges::range_reference_t<V>>
class join_view :
public ranges::view_interface<join_view<V>>
| (1) | (since C++20) |
namespace views {
inline constexpr /* unspecified */ join = /* unspecified */;
}
| (2) | (since C++20) |
view consisting of the sequence obtained from flattening a view of ranges.views::join(e) is expression-equivalent to join_view<views::all_t<decltype((e))>>{e} for any suitable subexpressions e.|
(C++20) | constructs a join_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) |
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) | the iterator type (exposition-only member class template) |
|
(C++20) | the sentinel type (exposition-only member class template) |
Before P2328R1 was adopted, the inner range type (ranges::range_reference_t<V>) cannot be a container type (but can be reference to container). For example, it was not allowed to join a transform_view of std::string prvalue.
struct Person { int age; std::string name; };
auto f(std::vector<Person>& v) {
// return v | std::views::transform([](auto& p){ return p.name; })
// | std::views::join; // error before P2328R1
return v | std::views::transform([](auto& p) -> std::string& { return p.name; })
| std::views::join; // OK
}#include <iostream>
#include <ranges>
#include <string_view>
#include <vector>
int main()
{
using namespace std::literals;
const auto bits = {"https:"sv, "//"sv, "cppreference"sv, "."sv, "com"sv};
for (char const c : bits | std::views::join)
std::cout << c;
std::cout << '\n';
const std::vector<std::vector<int>> v{{1, 2}, {3, 4, 5}, {6}, {7, 8, 9}};
auto jv = std::ranges::join_view(v);
for (int const e : jv)
std::cout << e << ' ';
std::cout << '\n';
}Output:
https://cppreference.com 1 2 3 4 5 6 7 8 9
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3474 | C++20 | views::join(e) returned a copy of e when e is a join_view | returns a nested join_view |
| P2328R1 | C++20 | non-view range prvalues could not be joined by join_view | made joinable |
|
(C++23) | a view consisting of the sequence obtained from flattening a view of ranges, with the delimiter in between elements (class template) (range adaptor object) |
|
(C++20) | a view over the subranges obtained from splitting another view using a delimiter (class template) (range adaptor object) |
|
(C++20) | a view over the subranges obtained from splitting another view using a delimiter (class template) (range adaptor object) |
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