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<title>Issue 3912: enumerate_view::iterator::operator- should be noexcept</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#WP">WP</a> status.</em></p>
<h3 id="3912"><a href="lwg-defects.html#3912">3912</a>. <code>enumerate_view::iterator::operator-</code> should be <code>noexcept</code></h3>
<p><b>Section:</b> 25.7.24.3 <a href="https://wg21.link/range.enumerate.iterator">[range.enumerate.iterator]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2023-03-27 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#range.enumerate.iterator">active issues</a> in [range.enumerate.iterator].</p>
<p><b>View all other</b> <a href="lwg-index.html#range.enumerate.iterator">issues</a> in [range.enumerate.iterator].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The distance between two <code>enumerate_view::iterator</code>
is calculated by subtracting two integers, which never throws.
</p>

<p><i>[2023-05-24; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after five votes in favour during reflector poll.
</p>

<p><i>[2023-06-17 Approved at June 2023 meeting in Varna. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3912"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4944" title=" Working Draft, Standard for Programming Language C++">N4944</a>.
</p>

<ol>
<li>
<p>
Modify 25.7.24.3 <a href="https://wg21.link/range.enumerate.iterator">[range.enumerate.iterator]</a> as indicated:
</p>
<blockquote>
<pre><code>
namespace std::ranges {
  template&lt;view V&gt;
    requires <i>range-with-movable-references</i>&lt;V&gt;
  template&lt;bool Const&gt;
  class enumerate_view&lt;V&gt;::<i>iterator</i> {
    [&hellip;]
    public:
    [&hellip;]
    friend constexpr difference_type operator-(const iterator&amp; x, const iterator&amp; y)<ins> noexcept</ins>;
    [&hellip;]
  }
  [&hellip;]
}
</code></pre>
[&hellip;]
<pre><code>
friend constexpr difference_type operator-(const iterator&amp; x, const iterator&amp; y)<ins> noexcept</ins>;
</code></pre>
<p>
-19- <i>Effects</i>:
Equivalent to: <code>return x.<i>pos_</i> - y.<i>pos_</i>;</code>
</p>
</blockquote>
</li>
</ol>





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