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### 3543. Definition of when `counted_iterators` refer to the same sequence isn't quite right

Section: 25.5.7.1 [counted.iterator] Status: WP Submitter: Tim Song Opened: 2021-04-21 Last modified: 2021-06-07

Priority: Not Prioritized

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Discussion:

25.5.7.1 [counted.iterator]/3 says:

> Two values `i1` and `i2` of types `counted_iterator<I1>` and `counted_iterator<I2>` refer to elements of the same sequence if and only if `next(i1.base(), i1.count())` and `next(i2.base(), i2.count())` refer to the same (possibly past-the-end) element.

However, some users of `counted_iterator` (such as `take_view`) don't guarantee that there are `count()` elements past `base()`. It seems that we need to rephrase this definition to account for such uses.

[2021-05-10; Reflector poll]

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

[2021-06-07 Approved at June 2021 virtual plenary. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4885.

1. Modify 25.5.7.1 [counted.iterator] as indicated:

   > -3- Two values `i1` and `i2` of types `counted_iterator<I1>` and `counted_iterator<I2>` refer to elements of the same sequence if and only if there exists some integer `n` such that `next(i1.base(), i1.count() + n)` and `next(i2.base(), i2.count() + n)` refer to the same (possibly past-the-end) element.