std::ranges::views::common, std::ranges::common_view

 

C++

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Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_t range_value_t	range_reference_trange_const_reference_trange_rvalue_reference_t   (C++23)	iterator_tconst_iterator_tsentinel_t (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty iota_viewviews::iota	single_viewviews::single basic_istream_viewviews::istream	repeat_viewviews::repeat (C++23)(C++23)
Adaptors
ref_view views::all_tviews::all common_viewviews::common owning_view views::counted reverse_viewviews::reverse zip_viewviews::zip (C++23)(C++23) as_const_viewviews::as_const (C++23)(C++23) as_rvalue_viewviews::as_rvalue (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while zip_transform_viewviews::zip_transform (C++23)(C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)   cartesian_product_viewviews::cartesian_product (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform adjacent_viewviews::adjacent (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) stride_viewviews::stride (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split join_with_viewviews::join_with (C++23)(C++23) chunk_viewviews::chunk (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23)
Range adaptor objects
Range adaptor closure objects
Helper items
copyable-box	simple-view

 

std::ranges::common_view

Member functions

common_view::common_view (C++20)

common_view::base (C++20)

common_view::begin (C++20)

common_view::end (C++20)

common_view::size (C++20)

Deduction guides

 

Defined in header <ranges>
template< ranges::view V >     requires (!ranges::common_range<V> && 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 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) Range adaptor object. 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.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Data members

Typical implementations of common_view only hold one non-static data member: the underlying view of type V.

Member functions

(constructor) (C++20)	constructs a common_view (public member function)
base (C++20)	returns a copy of the underlying (adapted) view (public member function)
begin (C++20)	returns an iterator to the beginning (public member function)
end (C++20)	returns an iterator to the end (public member function)
size (C++20)	returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (public member function)
Inherited from std::ranges::view_interface
empty (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>)
operator bool (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>)
data (C++20)	Gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function of std::ranges::view_interface<D>)
front (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>)
back (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>)
operator[] (C++20)	Returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

Helper templates

template<class T> inline constexpr bool enable_borrowed_range<std::ranges::common_view<T>> =     std::ranges::enable_borrowed_range<T>;		(since C++20)

This specialization of std::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

Run this code

#include <iostream>
#include <iterator>
#include <numeric>
#include <ranges>
#include <list>
 
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: "contiguous range" required
//  auto e4 = c2.data(); // error: "contiguous range" required
//  auto e5 = c2[0];     // error: "contiguous range" required
}

Possible output:

accumulate: 15
c1.front(): 1
c1.back(): 5
c1.data(): 0x400ec0
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

ranges::common_range (C++20)	specifies that a range has identical iterator and sentinel types (concept)
common_iterator (C++20)	adapts an iterator type and its sentinel into a common iterator type (class template)