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4012. common_view::begin/end are missing the simple-view check

Section: 25.7.20.2 [range.common.view] Status: WP Submitter: Hewill Kang Opened: 2023-11-11 Last modified: 2024-04-02

Priority: Not Prioritized

View all other issues in [range.common.view].

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Discussion:

common_view::begin/end have exactly the same implementation as their corresponding const versions, which implies that when the underlying V satisfies simple-view, it is sufficient to just provide const-qualified members.

[2024-03-11; Reflector poll]

Set status to Tentatively Ready after six votes in favour during reflector poll.

[Tokyo 2024-03-23; Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4964.

1. Modify 25.7.20.2 [range.common.view] as indicated:

   namespace std::ranges {
     template<view V>
       requires (!common_range<V> && copyable<iterator_t<V>>)
     class common_view : public view_interface<common_view<V>> {
     private:
       V base_ = V();  // exposition only
   
     public:
       […]
       constexpr auto begin() requires (!simple-view<V>) {
         if constexpr (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 (!simple-view<V>) {
         if constexpr (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_));
       }
   
       […]
     };
   […]
   }