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    CWG Issue 1025</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="1025"></A><H4>1025.
  
Use of a reference as a non-type template argument
</H4>
<B>Section: </B>13.4.3&#160; [<A href="https://wg21.link/temp.arg.nontype">temp.arg.nontype</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>2010-01-31<BR>


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

<P>The current wording of 13.4.3 [<A href="https://wg21.link/temp.arg.nontype#1">temp.arg.nontype</A>] paragraph 1 does
not prevent the use a reference as a non-type template argument.  It
simply requires</P>

<BLOCKQUOTE>

the address of an object or function with external linkage... expressed
as <TT>&amp;</TT> <I>id-expression</I>...

</BLOCKQUOTE>

<P>This would presumably (but unintentionally?) allow an example like
the following:</P>

<PRE>
    struct S { };
    template&lt;S*&gt; struct X { };
    S s;
    S&amp; ref = s;
    X&lt;&amp;ref&gt; xr;   // well-formed?
</PRE>

<P>The expression <TT>&amp;ref</TT> is not a constant expression, but
the current wording of 13.4.3 [<A href="https://wg21.link/temp.arg.nontype">temp.arg.nontype</A>] does not require a
constant expression.</P>

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

<P>Change 13.4.3 [<A href="https://wg21.link/temp.arg.nontype#1.3">temp.arg.nontype</A>] bullet 1.3 as follows:</P>

<UL><LI><P>
<INS>a constant expression (7.7 [<A href="https://wg21.link/expr.const">expr.const</A>]) that
designates</INS> the address of an object or function with external
linkage, including function templates and function <I>template-id</I>s
but excluding non-static class members, expressed (ignoring
parentheses) as <TT>&amp;</TT> <I>id-expression</I>, except that the
<TT>&amp;</TT> may be omitted if the name refers to a function or
array and shall be omitted if the corresponding
<I>template-parameter</I> is a reference; or</P></LI></UL>

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