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<title>Issue 3352: strong_equality isn't a thing</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++20">C++20</a> status.</em></p>
<h3 id="3352"><a href="lwg-defects.html#3352">3352</a>. <code>strong_equality</code> isn't a thing</h3>
<p><b>Section:</b> 23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2019-12-06 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>1
</p>
<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p>
<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
[tab:container.req] includes the row:
</p>
<blockquote>
<p>
<b>Expression:</b> <code>i &lt;=&gt; j</code>
<p/>
<b>Return Type:</b> <code>strong_ordering</code> if <code>X::iterator</code> meets the random access iterator requirements, 
otherwise <code>strong_equality</code>.
<p/>
<b>Complexity:</b> constant
</p>
</blockquote>
<p>
"<code>strong_equality</code>" is (now) a meaningless term that appears nowhere else in the working draft. Presumably 
we want to make the Return Type unconditionally <code>strong_ordering</code>, and require this expression to be 
valid only when <code>i</code> and <code>j</code> are random access iterators. It's not clear to me if the best way to 
do so would be to add a "<i>Constraints</i>" to the "Assertion/note/pre-/post-condition" column of this table row, 
or if we should pull the row out into yet another "conditionally-supported iterator requirements" table.
</p>

<p><i>[2019-12-21 Issue Prioritization]</i></p>

<p>Priority to 1 after reflector discussion.</p>

<p><i>[2020-02-10, Prague; David Olsen provides new wording based upon Tim Songs suggestion]</i></p>

<p><i>[2020-02 Moved to Immediate on Tuesday in Prague.]</i></p>



<p id="res-3352"><b>Proposed resolution:</b></p>

<blockquote>
<table border="1">
<caption>Table 71 &mdash; Container requirements [tab:container.req]</caption>
<tr style="text-align:center">
<th>Expression</th>
<th>Return type</th>
<th>Operational<br/>semantics</th>
<th>Assertion/note<br/>pre/post-condition</th>
<th>Complexity</th>
</tr>
<tr>
<td colspan="5" align="center">
<code>[&hellip;]</code>
</td>
</tr>
<tr>
<td>
<code>i &lt;=&gt; j</code>
</td>
<td>
<code>strong_ordering</code> <del>if<br/>
<code>X::iterator</code> meets the<br/>
random access iterator<br/>
requirements, otherwise<br/>
<code>strong_equality</code></del>
</td>
<td></td>
<td>
<ins><i>Constraints:</i> <code>X::iterator</code> meets the random access iterator requirements.</ins>
</td>
<td>
constant
</td>
</tr>

<tr>
<td colspan="5" align="center">
<code>[&hellip;]</code>
</td>
</tr>
</table>
</blockquote>




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