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2595. reverse_iterator::operator[]'s return type revisited

Section: 25.5.1.2 [reverse.iterator], 25.5.1.6 [reverse.iter.elem] Status: New Submitter: Robert Haberlach Opened: 2016-02-28 Last modified: 2021-06-06

Priority: 3

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Discussion:

Issue 386 changed the return type of reverse_iterator::operator[] to unspecified. However, as of N3066, the return type of a random access iterator's operator[] shall be convertible to reference; thus the return type of reverse_iterator::operator[] should be reference (and it is in all common implementations).

Suggested resolution: Adjust 25.5.1.2 [reverse.iterator]'s synopsis and 25.5.1.6 [reverse.iter.elem] to use reference instead of unspecified.

[2021-06-06 Tim syncs wording to current working draft]

Proposed resolution:

This wording is relative to N4885.

1. Edit 25.5.1.2 [reverse.iterator], class template synopsis, as indicated:

   namespace std {
     template <class Iterator>
     class reverse_iterator {
     public:
       […]
       using reference         = iter_reference_t<Iterator>;
       […]
       constexpr referenceunspecified operator[](difference_type n) const;
       […]
     };
   }
   

2. Change 25.5.1.6 [reverse.iter.elem] before p3 as indicated:

   constexpr referenceunspecified operator[](difference_type n) const;