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    CWG Issue 966</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="966"></A><H4>966.
  
Nested types without linkage
</H4>
<B>Section: </B>6.7&#160; [<A href="https://wg21.link/basic.link">basic.link</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Jason Merrill
 &#160;&#160;&#160;

 <B>Date: </B>15 September, 2009<BR>


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



<P>The recent changes to allow use of unnamed types as template
arguments require some rethinking of how unnamed types are treated
in general.  At least, a class-scope unnamed type should have the
same linkage as its containing class.  For example:</P>

<PRE>
    //<SPAN CLASS="cmnt"> File "hdr.h"</SPAN>
    struct S {
      static enum { No, Yes } locked;
    };
    template&lt;class T&gt; void f(T);

    //<SPAN CLASS="cmnt"> File "impl1.c"</SPAN>
    #include "hdr.h"
    template void f(decltype(S::locked));

    //<SPAN CLASS="cmnt"> File "impl2.c"</SPAN>
    #include "hdr.h"
    template void f(decltype(S::locked));
</PRE>

<P>The two explicit instantiation directives should refer to the
same specialization.</P>

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

<P>Change 6.7 [<A href="https://wg21.link/basic.link#8">basic.link</A>] paragraph 8 as follows:</P>

<BLOCKQUOTE>

<P>Names not covered by these rules have no linkage.  Moreover,
except as noted, a name declared in a local scope (6.4.3 [<A href="https://wg21.link/basic.scope.block">basic.scope.block</A>]) has no linkage. A type is said to have linkage if
and only if:</P>

<UL>
<LI><P>it is a class or enumeration type that is named (or
has a name for linkage purposes (9.2.4 [<A href="https://wg21.link/dcl.typedef">dcl.typedef</A>])) and
the name has linkage; or</P></LI>

<LI><P><INS>it is an unnamed class or enumeration member of a class
with linkage; or</INS></P></LI>

<LI><P>...</P></LI>

</UL>

</BLOCKQUOTE>

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