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3298. Range adaptors introduced by P1035 do not require viewable_range

Section: 26.7.9.2 [range.take.while.view], 26.7.10.2 [range.drop.view], 26.7.11.2 [range.drop.while.view] Status: NAD Submitter: Christopher Di Bella Opened: 2019-09-24 Last modified: 2020-09-06

Priority: Not Prioritized

View all other issues in [range.take.while.view].

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Discussion:

After adoption of P1035 range adaptor closure is described to take a viewable_range as input, and return a view as output. The deduction-guides for take_while_view, drop_view, and drop_while_view do not currently impose the viewable_range requirement.

[2020-02 Status to NAD on Thursday morning in Prague.]

Proposed resolution:

This wording is relative to N4830.

  1. Modify 26.7.9.2 [range.take.while.view], class template take_while_view synopsis, as indicated:

    namespace std::ranges {
      […]
      template<classinput_range R, class Pred>
        requires viewable_range<R> && 
            indirect_unary_predicate<const Pred, iterator_t<R>>
          take_while_view(R&&, Pred) -> take_while_view<all_view<R>, Pred>;
    }
    
  2. Modify 26.7.10.2 [range.drop.view], class template drop_view synopsis, as indicated:

    namespace std::ranges {
      […]
      template<classinput_range R>
        requires viewable_range<R>
          drop_view(R&&, range_difference_t<R>) -> drop_view<all_view<R>>;
    }
    
  3. Modify 26.7.11.2 [range.drop.while.view], class template drop_while_view synopsis, as indicated:

    namespace std::ranges {
      […]
      template<classinput_range R, class Pred>
        requires viewable_range<R> && 
            indirect_unary_predicate<const Pred, iterator_t<R>>
          drop_while_view(R&&, Pred) -> drop_while_view<all_view<R>, Pred>;
    }