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<title>Issue 1333: Missing forwarding during std::function invocation</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="1333"><a href="lwg-defects.html#1333">1333</a>. Missing forwarding during <code>std::function</code> invocation</h3>
<p><b>Section:</b> 22.10.17.3.5 <a href="https://wg21.link/func.wrap.func.inv">[func.wrap.func.inv]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2010-03-26 <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#func.wrap.func.inv">issues</a> in [func.wrap.func.inv].</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 current wording of 22.10.17.3.5 <a href="https://wg21.link/func.wrap.func.inv">[func.wrap.func.inv]</a>/1:
</p>

<blockquote><pre>
R operator()(ArgTypes... args) const
</pre>

<blockquote><p>
<i>Effects:</i> <code><i>INVOKE</i>(f, t1, t2, ..., tN, R)</code> (20.8.2), where
<code>f</code> is the target object (20.8.1) of <code>*this</code> and <code>t1, t2, ...,
tN</code> are the values in <code>args...</code>.
</p></blockquote>
</blockquote>

<p>
uses an unclear relation between the actual args and the used variables
<code>ti</code>. It should be made clear, that <code>std::forward</code> has to be used
to conserve the expression lvalueness.
</p>

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


<blockquote><p>
Moved to Tentatively Ready after 5 positive votes on c++std-lib.
</p></blockquote>

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




<p id="res-1333"><b>Proposed resolution:</b></p>
<p>
Change 22.10.17.3.5 <a href="https://wg21.link/func.wrap.func.inv">[func.wrap.func.inv]</a>/1+2 as indicated:
</p>

<blockquote><pre>
R operator()(ArgTypes... args) const
</pre>

<blockquote>
<p>
1 <i>Effects:</i>: <code><i>INVOKE</i>(f,
<ins>std::forward&lt;ArgTypes&gt;(args)...</ins><del>t1, t2, ..., tN</del>,
R)</code> (20.8.2), where <code>f</code> is the target object (20.8.1) of
<code>*this</code> <del>and <code>t1, t2, ..., tN</code> are the values in
<code>args...</code></del>.
</p>

<p>
2 <i>Returns:</i> Nothing if <code>R</code> is <code>void</code>, otherwise the return
value of <code><i>INVOKE</i>(f,
<ins>std::forward&lt;ArgTypes&gt;(args)...</ins><del>t1, t2, ..., tN</del>,
R)</code>.
</p>

<p>
3 <i>Throws:</i> <code>bad_function_call</code> if <code>!*this</code>; otherwise, any
exception thrown by the wrapped callable object.
</p>
</blockquote>
</blockquote>






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