A range adaptor that represents
view
consisting of the sequence obtained from flattening a view of ranges.
join_view models input_range.
join_view models forward_range when:
forward_range.join_view models bidirectional_range when:
bidirectional_range, andbidirectional_range and common_range.join_view models common_range when:
forward_range and common_range.join_view
sized_range or forward_range
std::ranges::view_interface<D>) [edit] returns a constant iterator to the beginning of the range
std::ranges::view_interface<D>) [edit] returns a sentinel for the constant iterator of the range
std::ranges::view_interface<D>) [edit] returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
std::ranges::view_interface<D>) [edit] returns the first element in the derived view, provided if it satisfies forward_range
std::ranges::view_interface<D>) [edit] returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range
std::ranges::view_interface<D>) [edit] [edit] Deduction guides [edit] Nested classes the iterator type
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
}[edit] Example
#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[edit] 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 3474 C++20 views::join(e) returned a copy of e when e is ajoin_view returns a nested join_view P2328R1 C++20 non-view range prvalues could not be joined by join_view made joinable [edit] See also
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