Issue 4245: Operators that interact with `counted_iterator` and `default_sentinel_t` should be `noexcept`

Title: Operators that interact with `counted_iterator` and `default_sentinel_t` should be `noexcept`
Status: wp
Section: [counted.iterator][counted.iter.nav][counted.iter.cmp]
Submitter: Hewill Kang

Created on 2025-04-18.00:00:00 last changed 2 weeks ago

Messages

Date: 2025-06-23.16:37:24

Proposed resolution:

This wording is relative to N5008.

Modify [counted.iterator] as indicated:

namespace std {
  template<input_or_output_iterator I>
  class counted_iterator {
  public:
    […]
    friend constexpr iter_difference_t<I> operator-(
      const counted_iterator& x, default_sentinel_t) noexcept;
    friend constexpr iter_difference_t<I> operator-(
      default_sentinel_t, const counted_iterator& y) noexcept;
    […]
    friend constexpr bool operator==(
      const counted_iterator& x, default_sentinel_t) noexcept;
    […]
  };
  […]
}

Modify [counted.iter.nav] as indicated:

friend constexpr iter_difference_t<I> operator-(
  const counted_iterator& x, default_sentinel_t) noexcept;

-15- Effects: Equivalent to: return -x.length;

friend constexpr iter_difference_t<I> operator-(
  default_sentinel_t, const counted_iterator& y) noexcept;

-16- Effects: Equivalent to: return y.length;

Modify [counted.iter.cmp] as indicated:

friend constexpr bool operator==(
  const counted_iterator& x, default_sentinel_t) noexcept;
-3- Effects: Equivalent to: return x.length == 0;

msg14804 (view)

Date: 2025-06-23.16:37:24

[ Sofia 2025-06-21; Status changed: Voting → WP. ]

msg14727 (view)

Date: 2025-06-15.00:00:00

[ 2025-06-12; Reflector poll ]

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

msg14726 (view)

Date: 2025-04-18.00:00:00

`counted_iterator` can be compared or subtracted from `default_sentinel_t`, which only involves simple integer arithmetic and does not have any Preconditions.

In this case, it is reasonable to declare them as noexcept.

History
Date	User	Action	Args
2025-06-23 16:37:24	admin	set	messages: + msg14864
2025-06-23 16:37:24	admin	set	status: voting -> wp
2025-06-12 20:59:27	admin	set	status: ready -> voting
2025-06-12 20:55:03	admin	set	messages: + msg14804
2025-06-12 20:55:03	admin	set	status: new -> ready
2025-04-21 10:17:51	admin	set	messages: + msg14727
2025-04-18 00:00:00	admin	create