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4573. Improve view_interface::cbegin

Section: 25.5.3 [view.interface] Status: New Submitter: Hewill Kang Opened: 2026-04-19 Last modified: 2026-05-29

Priority: 3

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Discussion:

The view_interface can provide only a const cbegin member when the derived class is simple-view, which helps reduce template instantiation.

[2026-05-29; Reflector poll.]

Set priority to 3 after reflector poll.

This does not seem to eliminate class template instantiations, so may not be an improvement. Would benefit from benchmarks.

We could go even further and replace !simple_range<R>, with !input_range<const R>, due to ranges::cbegin and ranges::cend using possibly-constant-range.

Proposed resolution:

This wording is relative to N5032.

1. Modify 25.5.3 [view.interface] as indicated:

   namespace std::ranges {
     template<class D>
       requires is_class_v<D> && same_as<D, remove_cv_t<D>>
     class view_interface {
       […]
     public:
       […]
       constexpr auto cbegin() requires input_range<D> && (!simple-view<D>) {
         return ranges::cbegin(derived());
       }
       constexpr auto cbegin() const requires input_range<const D> {
         return ranges::cbegin(derived());
       }
       constexpr auto cend() requires input_range<D> && (!simple-view<D>) {
         return ranges::cend(derived());
       }
       constexpr auto cend() const requires input_range<const D> {
         return ranges::cend(derived());
       }
       […]
     };
   }