This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of New status.

4561. reverse_view does not consider simple-view

Section: 25.7.21.2 [range.reverse.view] Status: New Submitter: Hewill Kang Opened: 2026-03-27 Last modified: 2026-04-04

Priority: Not Prioritized

View other active issues in [range.reverse.view].

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

View all issues with New status.

Discussion:

Currently, non-const begin/end for reverse_view are always provided.

However, when the underlying range is simple-view and common_view, we can just provide const begin to reduce the number of template instantiations.

And it is also reasonable to only provide const end in the case of simple-view for the same reason.

Proposed resolution:

This wording is relative to N5032.

1. Modify 25.7.21.2 [range.reverse.view] as indicated:

   namespace std::ranges {
     template<view V>
       requires bidirectional_range<V>
     class reverse_view : public view_interface<reverse_view<V>> {
       […]
       constexpr reverse_iterator<iterator_t<V>> begin()
         requires (!(simple-view<V> && common_range<const V>));
       constexpr reverse_iterator<iterator_t<V>> begin() requires common_range<V>;
       constexpr auto begin() const requires common_range<const V>;
   
       constexpr reverse_iterator<iterator_t<V>> end() requires (!simple-view<V>);
       constexpr auto end() const requires common_range<const V>;
       […]
     };
     […]
   }
   

   […]

   constexpr reverse_iterator<iterator_t<V>> begin()
     requires (!(simple-view<V> && common_range<const V>));
   

   -2-Returns:

   make_reverse_iterator(ranges::next(ranges::begin(base_), ranges::end(base_)))
   

   -3- Remarks: In order to provide the amortized constant time complexity required by the range concept, this function caches the result within the reverse_view for use on subsequent calls.

   constexpr reverse_iterator<iterator_t<V>> begin() requires common_range<V>;
   constexpr auto begin() const requires common_range<const V>;
   

   -4- Effects: Equivalent to: return make_reverse_iterator(ranges::end(base_));

   constexpr reverse_iterator<iterator_t<V>> end() requires (!simple-view<V>);
   constexpr auto end() const requires common_range<const V>;
   

   -5- Effects: Equivalent to: return make_reverse_iterator(ranges::begin(base_));