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4112. has-arrow should required operator->() to be const-qualified

Section: 25.5.2 [range.utility.helpers] Status: Voting Submitter: Hewill Kang Opened: 2024-06-22 Last modified: 2024-11-19

Priority: Not Prioritized

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Discussion:

The helper concept has-arrow in 25.5.2 [range.utility.helpers] does not require that I::operator->() be const-qualified, which is inconsistent with the constraints on reverse_iterator and common_iterator's operator->() as the latter two both require the underlying iterator has const operator->() member.

We should enhance the semantics of has-arrow so that implicit expression variations (18.2 [concepts.equality]) prohibit silly games.

[St. Louis 2024-06-24; move to Ready]

Proposed resolution:

This wording is relative to N4981.

1. Modify 25.5.2 [range.utility.helpers] as indicated:

   […]
   
   template<class I>
     concept has-arrow =                                       // exposition only
       input_iterator<I> && (is_pointer_v<I> || requires(const I i) { i.operator->(); });
   
   […]