<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1793</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<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="1793"></A><H4>1793.
  
<TT>thread_local</TT> in explicit specializations
</H4>
<B>Section: </B>9.2.2&#160; [<A href="https://wg21.link/dcl.stc">dcl.stc</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

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

 <B>Date: </B>2013-10-02<BR>


<P>[Moved to DR at the November, 2014 meeting.]</P>

<P>According to 9.2.2 [<A href="https://wg21.link/dcl.stc#1">dcl.stc</A>] paragraph 1,</P>

<BLOCKQUOTE>

...If <TT>thread_local</TT> appears in any declaration of a variable it
shall be present in all declarations of that
entity... A <I>storage-class-specifier</I> shall not be specified in an
explicit specialization (13.9.4 [<A href="https://wg21.link/temp.expl.spec">temp.expl.spec</A>]) or an explicit
instantiation (13.9.3 [<A href="https://wg21.link/temp.explicit">temp.explicit</A>]) directive.

</BLOCKQUOTE>

<P>These two requirements appear to be in conflict when an explicit
instantiation or explicit specialization names a <TT>thread_local</TT>
variable.  For example,</P>

<PRE>
  template &lt;class T&gt; struct S {
    thread_local static int tlm;
  };
  template &lt;&gt; int S&lt;int&gt;::tlm = 0;
  template &lt;&gt; thread_local int S&lt;float&gt;::tlm = 0;
</PRE>

<P>which of the two explicit specializations is correct?</P>

<P><B>Proposed resolution (February, 2014):</B></P>

<P>Change 9.2.2 [<A href="https://wg21.link/dcl.stc#1">dcl.stc</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

...A <I>storage-class-specifier</I> <INS>other
than <TT>thread_local</TT></INS> shall not be specified in an explicit
specialization (13.9.4 [<A href="https://wg21.link/temp.expl.spec">temp.expl.spec</A>]) or an explicit instantiation
(13.9.3 [<A href="https://wg21.link/temp.explicit">temp.explicit</A>]) directive.

</BLOCKQUOTE>

<BR><BR>
</BODY>
</HTML>
