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    CWG Issue 691</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="691"></A><H4>691.
  
Template parameter packs in class template partial specializations
</H4>
<B>Section: </B>13.2&#160; [<A href="https://wg21.link/temp.param">temp.param</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>Doug Gregor
 &#160;&#160;&#160;

 <B>Date: </B>9 April, 2008<BR>


<P>[Voted into WP at August, 2010 meeting.]</P>



<P>13.2 [<A href="https://wg21.link/temp.param#11">temp.param</A>] paragraph 11 currently says,</P>

<BLOCKQUOTE>

If a <I>template-parameter</I> of a class template is a template
parameter pack, it shall be the last
<I>template-parameter</I>. [<I>Note:</I> These are not
requirements for function templates because template arguments
might be deduced (13.10.3 [<A href="https://wg21.link/temp.deduct">temp.deduct</A>])...

</BLOCKQUOTE>

<P>This restriction was only meant to apply to primary class
templates, not partial specializations.</P>

<P>
<U>Suggested resolution</U>:</P>

<BLOCKQUOTE>

If a <I>template-parameter</I> of a <INS>primary</INS> class template
is a template parameter pack, it shall be the last
<I>template-parameter</I>. [<I>Note:</I> These are not
requirements for function templates <INS>or class template partial
specializations</INS> because template arguments might be deduced
(13.10.3 [<A href="https://wg21.link/temp.deduct">temp.deduct</A>])...

</BLOCKQUOTE>

<P><B>Proposed resolution (February, 2010):</B></P>

<P>Change 13.2 [<A href="https://wg21.link/temp.param#11">temp.param</A>] paragraph 11 as follows:</P>

<BLOCKQUOTE>

If a <I>template-parameter</I> of a class template has a default
<I>template-argument</I>, each subsequent
<I>template-parameter</I> shall either have a default
<I>template-argument</I> supplied or be a template parameter pack.  If a
<I>template-parameter</I> of a <INS>primary</INS> class template
is a template parameter pack, it shall be the last
<I>template-parameter</I>. [<I>Note:</I> These are not
requirements for function templates <INS>or class template partial
specializations</INS> because template arguments
<DEL>might</DEL> <INS>can</INS> be deduced (13.10.3 [<A href="https://wg21.link/temp.deduct">temp.deduct</A>]). [<I>Example:</I>...

</BLOCKQUOTE>

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