std::ranges::views::common, std::ranges::common_view
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(exposition-only member object*)
returns the approximate size of the resulting
(public member function) [edit]
returns a constant iterator to the beginning of the range
(public member function of
returns a sentinel for the constant iterator of the range
(public member function of
adapts an iterator type and its sentinel into a common iterator type
(class template) [edit]
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
common_viewviews::common
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
std::ranges::common_view
Defined in header
<ranges>
template< ranges::view V >
(1)
(since C++20)
requires (not ranges::common_range <V> and
std::copyable <ranges::iterator_t <V>>)
class common_view
namespace views {
(2)
(since C++20)
inline constexpr /* unspecified */ common = /* unspecified */;
Call signature
template< ranges::viewable_range R >
(since C++20)
requires /* see below */
1) Adapts a given
view with different types for iterator/sentinel pair into a view that is also a common_range. A common_view always has the same iterator/sentinel type.2) RangeAdaptorObject. Let e be a subexpression. Then the expression views::common(e) is expression-equivalent to:
- views::all (e), if it is a well-formed expression and decltype((e)) models
common_range; - common_view{e} otherwise.
Contents
[edit] Data members
Member
Description
V base_ (private)
the underlying view(exposition-only member object*)
[edit] Member functions
returns the number of elements, provided only if the underlying (adapted) range satisfies
(public member function) [edit]
sized_range (public member function) [edit]
(C++26)
approximately_sized_range (public member function) [edit]
Inherited from std::ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies
(public member function of
sized_range or forward_range (public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
(C++23)
(public member function of
std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of
(public member function of
std::ranges::view_interface<D>) [edit]
gets the address of derived view's data, provided only if its iterator type satisfies
(public member function of
contiguous_iterator (public member function of
std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies
(public member function of
forward_range (public member function of
std::ranges::view_interface<D>) [edit]
returns the last element in the derived view, provided only if it satisfies
(public member function of
bidirectional_range and common_range (public member function of
std::ranges::view_interface<D>) [edit]
returns the
(public member function of
nth element in the derived view, provided only if it satisfies random_access_range (public member function of
std::ranges::view_interface<D>) [edit]
[edit] Deduction guides
[edit] Helper templates
template< class T >
(since C++20)
constexpr bool enable_borrowed_range<std::ranges::common_view<T>> =
This specialization of ranges::enable_borrowed_range makes common_view satisfy borrowed_range when the underlying view satisfies it.
[edit] Notes
common_view can be useful for working with legacy algorithms that expect the iterator and sentinel are of the same type.
[edit] Example
Run this code
#include <initializer_list> #include <iostream> #include <iterator> #include <list> #include <numeric> #include <ranges> int main() { auto v1 = {1, 2, 3, 4, 5}; auto i1 = std::counted_iterator {v1.begin(), std::ssize (v1)}; auto r1 = std::ranges::subrange {i1, std::default_sentinel }; // auto e1 = std::accumulate(r1.begin(), r1.end(), 0); // error: "common range" required auto c1 = std::ranges::common_view{r1}; std::cout << "accumulate: " << std::accumulate (c1.begin(), c1.end(), 0) << '\n'; // inherited from ranges::view_interface: std::cout << "c1.front(): " << c1.front() << '\n'; std::cout << "c1.back(): " << c1.back() << '\n'; std::cout << "c1.data(): " << c1.data() << '\n'; std::cout << "c1[0]: " << c1[0] << '\n'; auto v2 = std::list {1, 2, 3, 4, 5}; auto i2 = std::counted_iterator {v2.begin(), std::ssize (v2)}; auto r2 = std::ranges::subrange {i2, std::default_sentinel }; // auto e2 = std::accumulate(r2.begin(), r2.end(), 0); // error: "common range" required auto c2 = std::ranges::common_view{ r2 }; std::cout << "accumulate: " << std::accumulate (c2.begin(), c2.end(), 0) << '\n'; // inherited from ranges::view_interface: std::cout << "c2.front(): " << c2.front() << '\n'; // auto e3 = c2.back(); // error: "bidirectional range" required // auto e4 = c2.data(); // error: "contiguous range" required // auto e5 = c2[0]; // error: "random access range" required }
Possible output:
accumulate: 15 c1.front(): 1 c1.back(): 5 c1.data(): 0x7f19937f00d0 c1[0]: 1 accumulate: 15 c2.front(): 1
[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 3494 | C++20 | common_view was never a borrowed_range
|
it is a borrowed_range if its underlying view is
|
[edit] See also
(C++20)
(class template) [edit]