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<title>Issue 819: rethrow_if_nested</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="819"><a href="lwg-defects.html#819">819</a>. rethrow_if_nested</h3>
<p><b>Section:</b> 17.9.8 <a href="https://wg21.link/except.nested">[except.nested]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2008-03-25 <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#except.nested">issues</a> in [except.nested].</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>
Looking at the wording I submitted for <code>rethrow_if_nested</code>, I don't think I
got it quite right.
</p>

<p>
The current wording says:
</p>

<blockquote>
<pre>
template &lt;class E&gt; void rethrow_if_nested(const E&amp; e);
</pre>
<blockquote>
<p>
<i>Effects:</i> Calls <code>e.rethrow_nested()</code> only if <code>e</code>
is publicly derived from <code>nested_exception</code>.
</p>
</blockquote>
</blockquote>

<p>
This is trying to be a bit subtle, by requiring <code>e</code> (not <code>E</code>) to be publicly
derived from <code>nested_exception</code> the idea is that a <code>dynamic_cast</code> would be
required to be sure.  Unfortunately, if <code>e</code> is dynamically but not statically
derived from <code>nested_exception</code>, <code>e.rethrow_nested()</code> is ill-formed.
</p>

<p><i>[
San Francisco:
]</i></p>


<blockquote><p>
Alisdair was volunteered to provide wording.
</p></blockquote>

<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
Leave as Open. Alisdair to provide wording.
</p></blockquote>

<p><i>[
2009-11-09 Alisdair provided wording.
]</i></p>


<p><i>[
2010-03-10 Dietmar updated wording.
]</i></p>


<p><i>[
2010 Pittsburgh:
]</i></p>


<blockquote><p>
Moved to Ready for Pittsburgh.
</p></blockquote>



<p id="res-819"><b>Proposed resolution:</b></p>
<p>
Change 17.9.8 <a href="https://wg21.link/except.nested">[except.nested]</a>, p8:
</p>

<blockquote><pre>
template &lt;class E&gt; void rethrow_if_nested(const E&amp; e);
</pre>
<blockquote><p>
-8- <i>Effects:</i> <del>Calls <code>e.rethrow_nested()</code>
o</del><ins>O</ins>nly if <ins>the dynamic type of</ins> <code>e</code> is
publicly <ins>and unambiguously</ins> derived from
<code>nested_exception</code> <ins>this calls
<code>dynamic_cast&lt;const nested_exception&amp;&gt;(e).rethrow_nested()</code></ins>.
</p></blockquote>
</blockquote>






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