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<title>Issue 1335: Insufficient requirements for tuple::operator&lt;()</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++11">C++11</a> status.</em></p>
<h3 id="1335"><a href="lwg-defects.html#1335">1335</a>. Insufficient requirements for <code>tuple::operator&lt;()</code></h3>
<p><b>Section:</b> 22.4.9 <a href="https://wg21.link/tuple.rel">[tuple.rel]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Joe Gottman <b>Opened:</b> 2010-05-15 <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#tuple.rel">active issues</a> in [tuple.rel].</p>
<p><b>View all other</b> <a href="lwg-index.html#tuple.rel">issues</a> in [tuple.rel].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The requirements section for <code>std::tuple</code> says the following: 
</p>

<blockquote><p>
<i>Requires:</i> For all <code>i</code>, where <code>0 &lt;= i and i &lt;
sizeof...(Types)</code>, <code>get&lt;i&gt;(t) &lt; get&lt;i&gt;(u)</code> is a valid
expression returning a type that is convertible to <code>bool</code>.
<code>sizeof...(TTypes) == sizeof...(UTypes)</code>.
</p></blockquote>

<p>
This is necessary but not sufficient, as the algorithm for comparing
<code>tuple</code>s also computes <code>get&lt;i&gt;(u) &lt; get&lt;i&gt;(t)</code>
(note the order)
</p>

<p><i>[
Post-Rapperswil
]</i></p>


<blockquote><p>
Moved to Tentatively Ready with updated wording correcting change-bars after 6 
positive votes on c++std-lib.
</p></blockquote>

<p><i>[
Adopted at 2010-11 Batavia
]</i></p>




<p id="res-1335"><b>Proposed resolution:</b></p>

<ol>
<li>Change [tuple.rel] before p. 4 as indicated [<strong>Remark to the editor: This paragraph doesn't have a number yet,
but it seems to me as if it should have one</strong>]:
<blockquote><pre>
template&lt;class... TTypes, class... UTypes&gt;
bool operator&lt;(const tuple&lt;TTypes...&gt;&amp; t, const tuple&lt;UTypes...&gt;&amp; u);
</pre>
<blockquote><p>
<em>Requires</em>: For all <code>i</code>, where <code>0 &lt;= i</code> and <code>i &lt; sizeof...(Types)</code>, 
<code>get&lt;i&gt;(t) &lt; get&lt;i&gt;(u)</code> <ins>and <code>get&lt;i&gt;(u) &lt; get&lt;i&gt;(t)</code></ins><del>is 
a valid expression returning a type that is</del><ins> are valid expressions returning types that 
are</ins> convertible to <code>bool</code>. <code>sizeof...(TTypes) == sizeof...(UTypes)</code>.
</p></blockquote></blockquote>
</li>
</ol>






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