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    CWG Issue 2650</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="2650"></A><H4>2650.
  
Incorrect example for ill-formed non-type template arguments
</H4>
<B>Section: </B>13.10.3.1&#160; [<A href="https://wg21.link/temp.deduct.general">temp.deduct.general</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++23
 &#160;&#160;&#160;

 <B>Submitter: </B>US
 &#160;&#160;&#160;

 <B>Date: </B>2022-11-03<BR><BR>


<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2720r0.pdf#US28-068">P2720R0 comment
  US&#160;28-068<BR></A>

<P>[Accepted as a DR at the November, 2022 meeting.]</P>

<P>
The example intends to illustrate that a class type cannot be the type
of a non-type template parameter (although the example is still
ill-formed because "T()" is interpreted as a function type).
</P>

<P><B>Proposed resolution (approved by CWG 2022-11-08):</B></P>

<P>Change in 13.10.3.1 [<A href="https://wg21.link/temp.deduct.general#11.8">temp.deduct.general</A>] bullet 11.8 as follows:</P>

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<LI>...</LI>
<LI>
Attempting to give an invalid type to a non-type template parameter.
[Example 13:

<PRE>
  template &lt;class T, T&gt; struct S {};
  template &lt;class T&gt; int f(S&lt;T, <DEL>T()</DEL><INS>T{}</INS>&gt;*);   <INS>//<SPAN CLASS="cmnt"> #1</SPAN></INS>
  class X {
    <INS>int m;</INS>
  };
  int i0 = f&lt;X&gt;(0);   <INS>//<SPAN CLASS="cmnt"> #1 uses a value of non-structural type </SPAN>X<SPAN CLASS="cmnt"> as a non-type template argument</SPAN></INS>
</PRE>

-- end example ]
</LI>

<LI>...</LI>

</UL>

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