std::ranges::views::join, std::ranges::join_view
From cppreference.com
| Defined in header <ranges>
|
||
| template< ranges::input_range V > requires ranges::view<V> and |
(1) | (since C++20) |
| namespace views { inline constexpr /* unspecified */ join = /* unspecified */; |
(2) | (since C++20) |
| Call signature |
||
| template< ranges::viewable_range R > requires /* see below */ |
(since C++20) | |
1) A range adaptor that represents
view consisting of the sequence obtained from flattening a view of ranges.2) RangeAdaptorObject (and also RangeAdaptorClosureObject). The expression views::join(e) is expression-equivalent to join_view<views::all_t<decltype((e))>>{e} for any suitable subexpressions e.
join_view models input_range.
join_view models forward_range when:
- ranges::range_reference_t<V> is a reference type, and
- V and ranges::range_reference_t<V> each model
forward_range.
join_view models bidirectional_range when:
- ranges::range_reference_t<V> is a reference type,
- V models
bidirectional_range, and - ranges::range_reference_t<V> models both
bidirectional_rangeandcommon_range.
join_view models common_range when:
- ranges::range_reference_t<V> is a reference type, and
- V and ranges::range_reference_t<V> each model
forward_rangeandcommon_range.
Member functions
constructs a join_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) | |
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>) | |
Deduction guides
Nested classes
| the iterator type (exposition-only member class template*) | |
| the sentinel type (exposition-only member class template*) |
Notes
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 }
Example
Run this code
#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
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 a join_view
|
returns a nested join_view
|
| P2328R1 | C++20 | non-view range prvalues could not be joined by join_view
|
made joinable |
See also
a view consisting of the sequence obtained from flattening a view of ranges, with the delimiter in between elements(class template) (range adaptor object) | |
a view consisting of concatenation of the adapted views(class template) (customization point object) |