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3592. lazy_split_view needs to check the simpleness of Pattern

Section: 26.7.16.2 [range.lazy.split.view] Status: WP Submitter: Tim Song Opened: 2021-09-15 Last modified: 2021-10-14

Priority: Not Prioritized

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Discussion:

For forward ranges, the non-const versions of lazy_split_view::begin() and lazy_split_view::end() returns an outer-iterator<simple-view<V>>, promoting to const if V models simple-view. However, this failed to take Pattern into account, even though that will also be accessed as const if const-promotion takes place. There is no requirement that const Pattern is a range, however.

[2021-09-24; Reflector poll]

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

[2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4892.

1. Modify 26.7.16.2 [range.lazy.split.view], class template lazy_split_view synopsis, as indicated:

   namespace std::ranges {
   
     […]
   
     template<input_range V, forward_range Pattern>
       requires view<V> && view<Pattern> &&
                indirectly_comparable<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to> &&
               (forward_range<V> || tiny-range<Pattern>)
     class lazy_split_view : public view_interface<lazy_split_view<V, Pattern>> {
     private:
       […]
     public:
       […]
   
       constexpr auto begin() {
         if constexpr (forward_range<V>)
           return outer-iterator<simple-view<V> &&
             simple-view<Pattern>>{*this, ranges::begin(base_)};
         else {
           current_ = ranges::begin(base_);
           return outer-iterator<false>{*this};
         }
       }
       
       […]
       
       constexpr auto end() requires forward_range<V> && common_range<V> {
         return outer-iterator<simple-view<V> &&
           simple-view<Pattern>>{*this, ranges::end(base_)};
       }
   
       […]
     };
     
     […]
     
   }