std::ranges::views::common, std::ranges::common_view
Defined in header <ranges> | ||
|---|---|---|
template< ranges::view V >
requires (not ranges::common_range<V> and
std::copyable<ranges::iterator_t<V>>)
class common_view
: public ranges::view_interface<common_view<V>>
| (1) | (since C++20) |
namespace views {
inline constexpr /* unspecified */ common = /* unspecified */;
}
| (2) | (since C++20) |
| Call signature | ||
template< ranges::viewable_range R >
requires /* see below */
constexpr ranges::view auto common( R&& r );
| (since C++20) |
1) Adapts a given
2) RangeAdaptorObject. Let 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.e be a subexpression. Then the expression views::common(e) is expression-equivalent to: -
views::all(e), if it is a well-formed expression anddecltype((e))modelscommon_range; -
common_view{e}otherwise.
Data members
| Member | Description |
|---|---|
V base_ (private) | the underlying view (exposition-only member object*) |
Member functions
constructs a common_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 to the end (public member function) |
|
returns the number of elements, provided only if the underlying (adapted) range satisfies sized_range (public member function) |
|
|
(C++26) | returns the approximate size of the resulting approximately_sized_range (public member function) |
Inherited from |
|
returns whether the derived view is empty, provided only 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 only if ranges::empty is applicable to it (public member function of std::ranges::view_interface<D>) |
|
gets the address of derived view's data, provided only if its iterator type satisfies contiguous_iterator (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 only if it satisfies bidirectional_range and common_range (public member function of std::ranges::view_interface<D>) |
|
returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface<D>) |
|
Deduction guides
Helper templates
template< class T >
constexpr bool enable_borrowed_range<std::ranges::common_view<T>> =
ranges::enable_borrowed_range<T>;
| (since C++20) |
This specialization of ranges::enable_borrowed_range makes common_view satisfy borrowed_range when the underlying view satisfies it.
Notes
common_view can be useful for working with legacy algorithms that expect the iterator and sentinel are of the same type.
Example
#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
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 |
See also
|
(C++20) | specifies that a range has identical iterator and sentinel types (concept) |
|
(C++20) | adapts an iterator type and its sentinel into a common iterator type (class template) |
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