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<title>Issue 3432: Missing requirement for comparison_category</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#C++23">C++23</a> status.</em></p>
<h3 id="3432"><a href="lwg-defects.html#3432">3432</a>. Missing requirement for <code>comparison_category</code></h3>
<p><b>Section:</b> 27.3.4 <a href="https://wg21.link/string.view.comparison">[string.view.comparison]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2020-04-19 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
It's not clear what happens if a program-defined character traits type
defines <code>comparison_category</code> as a synonym for <code>void</code>,
or some other bogus type.
</p>
<p>
Discussion on the LWG reflector settled on making it ill-formed at the
point of use.
</p>

<p><i>[2020-07-17; Moved to Ready in telecon]</i></p>

<p><i>[2020-11-09 Approved In November virtual meeting. Status changed: Ready &rarr; WP.]</i></p>



<p id="res-3432"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4861">N4861</a>.
</p>

<ol>
<li><p>Modify 27.3.4 <a href="https://wg21.link/string.view.comparison">[string.view.comparison]</a> by adding a new paragraph after p3:</p>

<blockquote class="note">
<p>
As result of reflector discussion we decided to make a drive-by fix in p3 below.
</p>
</blockquote>

<blockquote>
<pre>
template&lt;class charT, class traits&gt;
  constexpr <i>see below</i> operator&lt;=&gt;(basic_string_view&lt;charT, traits&gt; lhs,
                                  basic_string_view&lt;charT, traits&gt; rhs) noexcept;
</pre>
<blockquote>
<p>-3- Let <code>R</code> denote the type <code>traits::comparison_category</code> if <ins>that <i>qualified-id</i>
is valid and denotes a type (13.10.3 <a href="https://wg21.link/temp.deduct">[temp.deduct]</a>)</ins><del>it exists</del>, otherwise <code>R</code> 
is <code>weak_ordering</code>.</p>

<p><ins>-?- <i>Mandates:</i> <code>R</code> denotes a comparison category type (17.12.2 <a href="https://wg21.link/cmp.categories">[cmp.categories]</a>).</ins></p>

<p>-4- <i>Returns:</i> <code>static_cast&lt;R&gt;(lhs.compare(rhs) &lt;=&gt; 0)</code>.</p>
</blockquote>
</blockquote>
</li>
</ol>




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