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4441. ranges::rotate do not handle sized-but-not-sized-sentinel ranges correctly

Section: 26.7.11 [alg.rotate], 26.8.2.3 [partial.sort], 26.8.3 [alg.nth.element], 26.8.6 [alg.merge] Status: Immediate Submitter: Tomasz Kamiński Opened: 2025-11-03 Last modified: 2025-11-04

Priority: Not Prioritized

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Discussion:

These do not handle sized-but-not-sized-sentinel ranges correctly.

[Kona 2025-11-03; approved by LWG. Status changed: New → Immediate.]

Proposed resolution:

This wording is relative to N5014.

1. Modify 26.7.11 [alg.rotate] as indicated:

   template<execution-policy Ep, sized-random-access-range R>
     requires permutable<iterator_t<R>>
     borrowed_subrange_t<R> ranges::rotate(Ep&& exec, R&& r, iterator_t<R> middle);
   
   

   -6- Effects Equivalent to: return ranges::rotate(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r)ranges::begin(r) + ranges::distance(r));

   […]

   template<execution-policy Ep, sized-random-access-range R, sized-random-access-range OutR>
     requires indirectly_copyable<iterator_t<R>, iterator_t<OutR>>
     ranges::rotate_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
   	  ranges::rotate_copy(Ep&& exec, R&& r, iterator_t<R> middle, OutR&& result_r);
   

   -18- Effects Equivalent to: return ranges::rotate(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r)ranges::begin(r) + ranges::distance(r), ranges::begin(result_r), ranges::end(result_r)ranges::begin(result_r) + ranges::distance(result_r));

2. Modify 26.8.2.3 [partial.sort] as indicated:

   template<execution-policy Ep, sized-random-access-range R,
            class Comp = ranges::less, class Proj = identity>
     requires sortable<iterator_t<R>, Comp, Proj>
     borrowed_iterator_t<R>
       ranges::partial_sort(Ep&& exec, R&& r, iterator_t<R> middle, Comp comp = {},
                            Proj proj = {});
   

   -7- Effects Equivalent to: return ranges::partial_sort(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r)ranges::begin(r) + ranges::distance(r), comp, proj);

3. Modify 26.8.3 [alg.nth.element] as indicated:

   template<execution-policy Ep, sized-random-access-range R, class Comp = ranges::less,
            class Proj = identity>
     requires sortable<iterator_t<R>, Comp, Proj>
     borrowed_iterator_t<R>
       ranges::nth_element(Ep&& exec, R&& r, iterator_t<R> nth, Comp comp = {}, Proj proj = {});
   

   -7- Effects Equivalent to: return ranges::nth_element(std::forward<Ep>(exec), ranges::begin(r), nth, ranges::end(r)ranges::begin(r) + ranges::distance(r), comp, proj);

4. Modify 26.8.6 [alg.merge] as indicated:

   template<execution-policy Ep, sized-random-access-range R, class Comp = ranges::less,
            class Proj = identity>
     requires sortable<iterator_t<R>, Comp, Proj>
     borrowed_iterator_t<R>
       ranges::inplace_merge(Ep&& exec, R&& r, iterator_t<R> middle, Comp comp = {},
                             Proj proj = {});
   

   -14- Effects Equivalent to: return ranges::inplace_merge(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r)ranges::begin(r) + ranges::distance(r), comp, proj);