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<title>Issue 4031: bad_expected_access&lt;void&gt; member functions 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="4031"><a href="lwg-defects.html#4031">4031</a>. <code>bad_expected_access&lt;void&gt;</code> member functions should be <code>noexcept</code></h3>
<p><b>Section:</b> 22.8.5 <a href="https://wg21.link/expected.bad.void">[expected.bad.void]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Cassio Neri <b>Opened:</b> 2023-12-24 <b>Last modified:</b> 2024-04-02</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
According to 17.9.3 <a href="https://wg21.link/exception">[exception]</a>/2:
</p>
<blockquote>
<p>
Each standard library class <code>T</code> that derives from class <code>exception</code> has the following 
publicly accessible member functions, each of them having a non-throwing exception specification (14.5):
</p>
<ol style="list-style-type: none">
<li><p>(2.1) &mdash; default constructor (unless the class synopsis shows other constructors)</p></li>
<li><p>(2.2) &mdash; copy constructor</p></li>
<li><p>(2.3) &mdash; copy assignment operator</p></li>
</ol>
</blockquote>
<p>
For good reasons, <code>bad_expected_access&lt;void&gt;</code> overrules from this general rule by 
protecting its special member functions. However, there's no reason these functions should not be 
<code>noexcept</code>.
</p>

<p><i>[2024-03-12; Reflector poll]</i></p>

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

<p><i>[Tokyo 2024-03-23; Status changed: Voting &rarr; WP.]</i></p>



<p id="res-4031"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4971" title=" Working Draft, Programming Languages — C++">N4971</a>.
</p>

<ol>

<li><p>Modify 22.8.5 <a href="https://wg21.link/expected.bad.void">[expected.bad.void]</a> as indicated:</p>

<blockquote>
<pre>
namespace std {
  template&lt;&gt;
  class bad_expected_access&lt;void&gt; : public exception {
  protected:
    bad_expected_access() noexcept;
    bad_expected_access(const bad_expected_access&amp;) <ins>noexcept</ins>;
    bad_expected_access(bad_expected_access&amp;&amp;) <ins>noexcept</ins>;
    bad_expected_access&amp; operator=(const bad_expected_access&amp;) <ins>noexcept</ins>;
    bad_expected_access&amp; operator=(bad_expected_access&amp;&amp;) <ins>noexcept</ins>;
    ~bad_expected_access();
  public:
    const char* what() const noexcept override;
  };
}
</pre>
</blockquote>

</li>

</ol>







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