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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#Dup">Dup</a> status.</em></p>
<h3 id="1230"><a href="lwg-closed.html#1230">1230</a>. <code>mem_fn</code> and variadic templates</h3>
<p><b>Section:</b> 22.10.16 <a href="https://wg21.link/func.memfn">[func.memfn]</a> <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-10-09 <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.memfn">issues</a> in [func.memfn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p>
<p><b>Duplicate of:</b> <a href="lwg-defects.html#920" title="Ref-qualification support in the library (Status: C++11)">920</a></p>
<p><b>Discussion:</b></p>



<p>
Since we have removed the entry in B <a href="https://wg21.link/implimits">[implimits]</a> for the
library-specific limit for number of arguments passed to
<code>function</code>/<code>tuple</code>/etc. I believe we need to update the
spec for <code>mem_fn</code> to reflect this.
</p>

<p>
The "<i>Remarks:</i> Implementations may implement <code>mem_fn</code> as a set of
overloaded function templates." no longer holds, as we cannot create an
arbitrary number of such overloads.  I believe we should strike the
remark and add a second signature:
</p>

<blockquote><pre>
template&lt;class R, class T, typename ... ArgTypes&gt;
  unspecified mem_fn(R (T::*pm)(ArgTypes...));
</pre></blockquote>

<p>
I believe we need two signatures as pointer-to-data-member and
pointer-to-member-function-taking-no-args appear to use subtly different
syntax.
</p>

<p><i>[
<a href="lwg-defects.html#920" title="Ref-qualification support in the library (Status: C++11)">920</a><sup><a href="https://cplusplus.github.io/LWG/issue920" title="Latest snapshot">(i)</a></sup> as a similar proposed resolution.
]</i></p>



<p id="res-1230"><b>Proposed resolution:</b></p>
<p>
Add to 22.10 <a href="https://wg21.link/function.objects">[function.objects]</a> and 22.10.16 <a href="https://wg21.link/func.memfn">[func.memfn]</a>:
</p>
<blockquote><pre>
template&lt;class R, class T&gt; <i>unspecified</i> mem_fn(R T::* pm)

<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...));</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile);</ins>

<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...)&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile&amp;);</ins>

<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...)&amp;&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const&amp;&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile&amp;&amp;);</ins>
<ins>template&lt;class R, class T, class ...Args&gt; <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile&amp;&amp;);</ins>
</pre></blockquote>

<p>
Strike 22.10.16 <a href="https://wg21.link/func.memfn">[func.memfn]</a>, p5:
</p>

<blockquote><p>
<del><i>Remarks:</i> Implementations may implement <code>mem_fn</code> as a set
of overloaded function templates.</del>
</p></blockquote>






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