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<title>Issue 4115: move_iterator::operator* should have conditional noexcept specification</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#New">New</a> status.</em></p>
<h3 id="4115"><a href="lwg-active.html#4115">4115</a>. <code>move_iterator::operator*</code> should have conditional <code>noexcept</code> specification</h3>
<p><b>Section:</b> 24.5.4.6 <a href="https://wg21.link/move.iter.elem">[move.iter.elem]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2024-07-03 <b>Last modified:</b> 2024-08-02</p>
<p><b>Priority: </b>4
</p>
<p><b>View all other</b> <a href="lwg-index.html#move.iter.elem">issues</a> in [move.iter.elem].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
For <code>move_iterator</code>, dereferencing it is actually equivalent to applying <code>iter_move</code> to it.
<p/>
However, unlike the latter, <code>move_iterator</code>'s dereference operator lacks a <code>noexcept</code> 
specification, which seems to be an oversight given that the standard goes to such great lengths to 
preserve the noexceptness of <code>iter_move</code>, and the main purpose of <code>move_iterator</code> is 
precisely to apply <code>iter_move</code> to the underlying iterator via dereferencing.
</p>

<p><i>[2024-08-02; Reflector poll]</i></p>

<p>
Set priority to 4 after reflector poll.
"Do we have evidence conditional noexcept matters here?
Do we have a policy that <code class='backtick'>operator*</code> should be noexcept whenever possible?
What criteria are we using to decide here?"
</p>



<p id="res-4115"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4981" title=" Working Draft, Programming Languages — C++">N4981</a>.
</p>

<ol>
<li><p>Modify 24.5.4.2 <a href="https://wg21.link/move.iterator">[move.iterator]</a> as indicated:</p>

<blockquote><pre>
namespace std {
  template&lt;class Iterator&gt;
  class move_iterator {
  public:
    [&hellip;]
    constexpr reference operator*() const <ins>noexcept(noexcept(ranges::iter_move(current)))</ins>;
    [&hellip;]
  };
}
</pre></blockquote>

</li>

<li><p>Modify 24.5.4.6 <a href="https://wg21.link/move.iter.elem">[move.iter.elem]</a> as indicated:</p>

<blockquote>
<pre>
constexpr reference operator*() const <ins>noexcept(noexcept(ranges::iter_move(current)))</ins>;
</pre>
<blockquote>
<p>
-1- <i>Effects</i>: Equivalent to: <code>return ranges::iter_move(current);</code>
</p>
</blockquote>
</blockquote>

</li>
</ol>





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