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3389. A move-only iterator still does not have a counted_iterator

Section: 25.5.7.2 [counted.iter.const] Status: C++20 Submitter: Patrick Palka Opened: 2020-02-07 Last modified: 2021-02-25

Priority: 0

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Discussion:

P1207R4 ("Movability of single-pass iterators") introduces the notion of a move-only non-forward iterator and makes some changes to the iterator adaptor counted_iterator in order to support move-only iterators.

The problem is that the constructor of counted_iterator (25.5.7.2 [counted.iter.const] p2) accepting such an iterator is specified as "Initializes current with i" which would attempt copy-constructing current from i instead of move-constructing it.

[2020-02 Prioritized as IMMEDIATE Monday morning in Prague]

Proposed resolution:

This wording is relative to N4849.

1. Modify 25.5.7.2 [counted.iter.const] as indicated:

   constexpr counted_iterator(I i, iter_difference_t<I> n);
   

   -1- Preconditions: n >= 0.

   -2- Effects: Initializes current with std::move(i) and length with n.