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3912. enumerate_view::iterator::operator- should be noexcept

Section: 25.7.24.3 [range.enumerate.iterator] Status: WP Submitter: Hewill Kang Opened: 2023-03-27 Last modified: 2023-11-22

Priority: Not Prioritized

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Discussion:

The distance between two enumerate_view::iterator is calculated by subtracting two integers, which never throws.

[2023-05-24; Reflector poll]

Set status to Tentatively Ready after five votes in favour during reflector poll.

[2023-06-17 Approved at June 2023 meeting in Varna. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4944.

1. Modify 25.7.24.3 [range.enumerate.iterator] as indicated:

   
   namespace std::ranges {
     template<view V>
       requires range-with-movable-references<V>
     template<bool Const>
     class enumerate_view<V>::iterator {
       […]
       public:
       […]
       friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept;
       […]
     }
     […]
   }
   

   […]

   
   friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept;
   

   -19- Effects: Equivalent to: return x.pos_ - y.pos_;