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4115. move_iterator::operator* should have conditional noexcept specification

Section: 25.5.4.6 [move.iter.elem] Status: New Submitter: Hewill Kang Opened: 2024-07-03 Last modified: 2024-08-02

Priority: 4

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Discussion:

For move_iterator, dereferencing it is actually equivalent to applying iter_move to it.

However, unlike the latter, move_iterator's dereference operator lacks a noexcept specification, which seems to be an oversight given that the standard goes to such great lengths to preserve the noexceptness of iter_move, and the main purpose of move_iterator is precisely to apply iter_move to the underlying iterator via dereferencing.

[2024-08-02; Reflector poll]

Set priority to 4 after reflector poll. "Do we have evidence conditional noexcept matters here? Do we have a policy that operator* should be noexcept whenever possible? What criteria are we using to decide here?"

Proposed resolution:

This wording is relative to N4981.

1. Modify 25.5.4.2 [move.iterator] as indicated:

   namespace std {
     template<class Iterator>
     class move_iterator {
     public:
       […]
       constexpr reference operator*() const noexcept(noexcept(ranges::iter_move(current)));
       […]
     };
   }
   

2. Modify 25.5.4.6 [move.iter.elem] as indicated:

   constexpr reference operator*() const noexcept(noexcept(ranges::iter_move(current)));
   

   -1- Effects: Equivalent to: return ranges::iter_move(current);