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    CWG Issue 1388</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="1388"></A><H4>1388.
  
Missing non-deduced context following a function parameter pack
</H4>
<B>Section: </B>13.10.3.2&#160; [<A href="https://wg21.link/temp.deduct.call">temp.deduct.call</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD3
 &#160;&#160;&#160;

 <B>Submitter: </B>James Widman
 &#160;&#160;&#160;

 <B>Date: </B>2011-09-02<BR>


<P>[Moved to DR at the October, 2012 meeting.]</P>



<P>Presumably 13.10.3.6 [<A href="https://wg21.link/temp.deduct.type#5">temp.deduct.type</A>] paragraph 5 should include a
bullet for a function parameter or function parameter pack that follows a
function parameter pack.</P>

<P><B>Proposed resolution (February, 2012):</B></P>

<P>Change 13.10.3.2 [<A href="https://wg21.link/temp.deduct.call#1">temp.deduct.call</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

<P>...<DEL>For a function parameter pack that does not occur at the end of
the <I>parameter-declaration-list</I>, the type of the parameter pack is a
non-deduced context.</DEL> <INS>When a function parameter pack appears in a
non-deduced context (13.10.3.6 [<A href="https://wg21.link/temp.deduct.type">temp.deduct.type</A>]), the type of that
parameter pack is never deduced.</INS> [<I>Example:</I>
</P>

<PRE>
  template&lt;class ... Types&gt; void f(Types&amp; ...);
  template&lt;class T1, class ... Types&gt; void g(T1, Types ...);
<INS>  template&lt;class T1, class ... Types&gt; void g1(Types ..., T1);</INS>

  void h(int x, float&amp; y) {
    const int z = x;
    f(x, y, z);                  //<SPAN CLASS="cmnt"> </SPAN>Types<SPAN CLASS="cmnt"> is deduced to </SPAN>int, float, const int
    g(x, y, z);                  //<SPAN CLASS="cmnt"> </SPAN>T1<SPAN CLASS="cmnt"> is deduced to </SPAN>int<SPAN CLASS="cmnt">; </SPAN>Types<SPAN CLASS="cmnt"> is deduced to </SPAN>float, int
<INS>    g1(x, y, z);                 //<SPAN CLASS="cmnt"> error: </SPAN>Types<SPAN CLASS="cmnt"> is not deduced</SPAN>
    g1&lt;int, int, int&gt;(x, y, z);  //<SPAN CLASS="cmnt"> OK, no deduction occurs</SPAN></INS>
  }
</PRE>

<P>&#8212;<I>end example</I>]</P>

</BLOCKQUOTE>

<P>This resolution also resolves <A HREF="1399.html">issue 1399</A>.</P>

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