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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;