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<title>Issue 914: Superfluous requirement for unique</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#NAD_Concepts">NAD Concepts</a> status.</em></p>
<h3 id="914"><a href="lwg-closed.html#914">914</a>. Superfluous requirement for unique</h3>
<p><b>Section:</b> 26.7.9 <a href="https://wg21.link/alg.unique">[alg.unique]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Concepts">NAD Concepts</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2008-10-03 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#alg.unique">active issues</a> in [alg.unique].</p>
<p><b>View all other</b> <a href="lwg-index.html#alg.unique">issues</a> in [alg.unique].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p>
<p><b>Discussion:</b></p>
<p>
26.7.9 <a href="https://wg21.link/alg.unique">[alg.unique]</a>/2: "Requires: The comparison function shall be an
equivalence relation."
</p>

<p>
The essence of this is already covered by the given requirement
</p>

<blockquote><pre>
EquivalenceRelation&lt;auto, Iter::value_type&gt; Pred
</pre></blockquote>

<p>
and should thus be removed.
</p>

<p><i>[
Batavia (2009-05):
]</i></p>

<blockquote><p>
We agree with the proposed resolution.
Move to Tentatively Ready.
</p></blockquote>


<p id="res-914"><b>Proposed resolution:</b></p>
<p>
Remove 26.7.9 <a href="https://wg21.link/alg.unique">[alg.unique]</a>/2
</p>

<blockquote><pre>
template&lt;ForwardIterator Iter&gt;
  requires OutputIterator&lt;Iter, Iter::reference&gt;
        &amp;&amp; EqualityComparable&lt;Iter::value_type&gt;
  Iter unique(Iter first, Iter last);

template&lt;ForwardIterator Iter, EquivalenceRelation&lt;auto, Iter::value_type&gt; Pred&gt;
  requires OutputIterator&lt;Iter, RvalueOf&lt;Iter::reference&gt;::type&gt;
        &amp;&amp; CopyConstructible&lt;Pred&gt;
  Iter unique(Iter first, Iter last,
               Pred pred);
</pre>
<blockquote>
<p>
1 <i>Effects:</i> ...
</p>
<p>
<del>2 <i>Requires:</i> The comparison function shall be an equivalence relation.</del>
</p>
</blockquote>
</blockquote>





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