[ranges] common_view takes a view which has different types for its iterator and sentinel and turns it into a view of the same elements with an iterator and sentinel of the same type.
[Note 1 :
common_view is useful for calling legacy algorithms that expect a range's iterator and sentinel types to be the same.
— _end note_]
Given a subexpression E, the expression views::common(E) is expression-equivalent to:
views::all(E), if decltype((E)) models common_range and views::all(E) is a well-formed expression.
Otherwise, common_view{E}.
[Example 1 : template<class ForwardIterator>size_t count(ForwardIterator first, ForwardIterator last);template<forward_range R> void my_algo(R&& r) { auto&& common = views::common(r);auto cnt = count(common.begin(), common.end());} — _end example_]
namespace std::ranges { template<view V> requires (copyable <iterator_t<V>>) class common_view : public view_interface<common_view<V>> { private: V base_ = V(); public: common_view() requires default_initializable <V> = default;constexpr explicit common_view(V r);constexpr V base() const & requires copy_constructible <V> { return base_ ; } constexpr V base() && { return std::move(base_ ); } constexpr auto begin() requires (random_access_range <V> && sized_range <V>) return ranges::begin(base_ );else return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::begin(base_ ));} constexpr auto begin() const requires range <const V> { if constexpr (random_access_range <const V> && sized_range <const V>) return ranges::begin(base_ );else return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::begin(base_ ));} constexpr auto end() requires (random_access_range <V> && sized_range <V>) return ranges::begin(base_ ) + ranges::distance(base_ );else return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::end(base_ ));} constexpr auto end() const requires range <const V> { if constexpr (random_access_range <const V> && sized_range <const V>) return ranges::begin(base_ ) + ranges::distance(base_ );else return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::end(base_ ));} constexpr auto size() requires sized_range <V> { return ranges::size(base_ );} constexpr auto size() const requires sized_range <const V> { return ranges::size(base_ );} constexpr auto reserve_hint() requires approximately_sized_range <V> { return ranges::reserve_hint(base_ );} constexpr auto reserve_hint() const requires approximately_sized_range <const V> { return ranges::reserve_hint(base_ );} };template<class R> common_view(R&&) -> common_view<views::all_t<R>>;}
constexpr explicit common_view(V base);
Effects : Initializes base_ with std::move(base).