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<title>Issue 678: Changes for [rand.req.eng]</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#CD1">CD1</a> status.</em></p>
<h3 id="678"><a href="lwg-defects.html#678">678</a>. Changes for [rand.req.eng]</h3>
<p><b>Section:</b> 29.5.3.4 <a href="https://wg21.link/rand.req.eng">[rand.req.eng]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Charles Karney <b>Opened:</b> 2007-05-15 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#rand.req.eng">issues</a> in [rand.req.eng].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Section 29.5.3.4 <a href="https://wg21.link/rand.req.eng">[rand.req.eng]</a> Random number engine requirements:
</p>

<p>
This change follows naturally from the proposed change to
<code>seed_seq::randomize</code> in <a href="lwg-defects.html#677" title="Weaknesses in seed_seq::randomize [rand.util.seedseq] (Status: CD1)">677</a><sup><a href="https://cplusplus.github.io/LWG/issue677" title="Latest snapshot">(i)</a></sup>.
</p>

<p>
In table 104 the description of <code>X(q)</code> contains a special treatment of
the case <code>q.size() == 0</code>.  This is undesirable for 4 reasons:
</p>

<ol>
<li>It replicates the functionality provided by <code>X()</code>.</li>
<li>It leads to the possibility of a collision in the state provided
    by some other <code>X(q)</code> with <code>q.size() &gt; 0</code>.</li>
<li>It is inconsistent with the description of the <code>X(q)</code> in
paragraphs 29.5.4.2 <a href="https://wg21.link/rand.eng.lcong">[rand.eng.lcong]</a> p5, 29.5.4.3 <a href="https://wg21.link/rand.eng.mers">[rand.eng.mers]</a> p8, and 29.5.4.4 <a href="https://wg21.link/rand.eng.sub">[rand.eng.sub]</a> p10 where
there is no special treatment of <code>q.size() == 0</code>.</li>
<li>The proposed replacement for <code>seed_seq::randomize</code> given above
    allows for the case <code>q.size() == 0</code>.</li>
</ol>

<p>
See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2391.pdf">N2391</a> and
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2423.pdf">N2423</a>
for some further discussion.
</p>


<p id="res-678"><b>Proposed resolution:</b></p>
<p>
Adopt the proposed resolution in
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2423.pdf">N2423</a>.
</p>


<p><i>[
Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue.
The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona.
]</i></p>





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