Proposed resolution:

This wording is relative to N5032.

1. Modify [range.concat.view] as indicated:

   namespace std::ranges {
     […]
     template<input_range... Views>
       requires (view<Views> && ...) && (sizeof...(Views) > 0) &&
                 concatable<Views...>
     class concat_view : public view_interface<concat_view<Views...>> {
       […]
       constexpr auto size() requires (sized_range<Views> && ...);
       constexpr auto size() const requires (sized_range<const Views> && ...);
       constexpr auto reserve_hint() requires (approximately_sized_range<Views> && ...);
       constexpr auto reserve_hint() const requires (approximately_sized_range<const Views> && ...);
     };
   }
   […]
   
   constexpr auto size() requires (sized_range<Views> && ...);
   constexpr auto size() const requires (sized_range<const Views> && ...);
   
   -8- Effects: Equivalent to:
   
   return apply(
     [](auto... sizes) {
       using CT = make-unsigned-like-t<common_type_t<decltype(sizes)...>>;
       return (CT(sizes) + ...);
     },
     tuple-transform(ranges::size, views_));
   
   
   
   constexpr auto reserve_hint() requires (approximately_sized_range<Views> && ...);
   constexpr auto reserve_hint() const requires (approximately_sized_range<const Views> && ...);
   
   -9- Effects: Equivalent to:
   
   return apply(
     [](auto... sizes) {
       using CT = make-unsigned-like-t<common_type_t<decltype(sizes)...>>;
       return (CT(sizes) + ...);
     },
     tuple-transform(ranges::reserve_hint, views_));
   
   
   
   

[ Croydon 2026-03-24; move to Immediate ]

Addresses FR-025-246

LEWG approved the NB comment "FR-025-246 25.7.18.2 Add a `reserve_hint` function to `concat_view`" without wording. This issue proposes the wording.