update

Author: jensmaurer

issues/2917.html

@@ -16,7 +16,7 @@
   Core Issues List revision 115a.
   See http://www.open-std.org/jtc1/sc22/wg21/ for the official
   list.</EM></P>
-<P>2024-08-07</P>
+<P>2024-08-17</P>
 <HR>
 <A NAME="2917"></A><H4>2917.
 
@@ -25,13 +25,15 @@
 <B>Section: </B>13.1&#160; [<A href="https://wg21.link/temp.pre">temp.pre</A>]
  &#160;&#160;&#160;
 
- <B>Status: </B>open
+ <B>Status: </B>review
  &#160;&#160;&#160;
 
  <B>Submitter: </B>Ambrose T
  &#160;&#160;&#160;
 
- <B>Date: </B>2024-07-30<BR>
+ <B>Date: </B>2024-07-30
+  &#160;&#160;&#160;
+  <B>Liaison: </B>EWG<BR>
 
 
 <P>(From submissions
@@ -63,7 +65,7 @@
   };
 </PRE>
 
-<P><U>Suggested resolution:</U></P>
+<P><B>Proposed resolution (2024-08-16):</B></P>
 
 <P>(<A HREF="2862.html">Issue 2862</A> modifies the same paragraph.)</P>
 
@@ -78,10 +80,8 @@
 <INS>In a <I>template-declaration</I> whose <I>declaration</I> is
 a <I>friend-type-declaration</I>,
 the <I>friend-type-specifier-list</I> shall consist of exactly
-one <I>friend-type-specifier</I>; if it is a pack expansion
-(13.7.4 [<A href="https://wg21.link/temp.variadic">temp.variadic</A>]), any packs expanded by that pack
-expansion shall not have been introduced by
-the <I>template-declaration</I>.  [ Example:</INS>
+one <I>friend-type-specifier</I> that is not a pack expansion.  [
+Example:</INS>
 
 <PRE class="ins">
 template&lt;class ...&gt;
@@ -100,6 +100,50 @@
 <INS>-- end example ]</INS>
 
 </BLOCKQUOTE>
+
+<P><B>CWG 2024-08-16</B></P>
+
+<P>The proposed resolution above disallows a few examples from paper
+<A HREF="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2893r3.html">P2893R3</A>
+(Variadic friends), such as
+</P>
+
+<PRE>
+  template&lt;class... Ts&gt;
+  struct VS {
+    template&lt;class U&gt;
+    friend class C&lt;Ts&gt;::Nested...; //<SPAN CLASS="cmnt"> now ill-formed</SPAN>
+  };
+</PRE>
+
+<P>The adopted wording for P2893R3 makes
+the <I>friend-type-specifier</I> (not the
+entire <I>template-declaration</I>) the pattern that is expanded by
+the pack expansion, leading to the expansion
+</P>
+
+<PRE>
+  struct VS&lt;T1, T2, T3&gt; {
+    template&lt;class U&gt;
+    friend class C&lt;T1&gt;::Nested, class C&lt;T2&gt;::Nested, class C&lt;T3&gt;::Nested;
+  };
+</PRE>
+
+<P>However, that violates the principle that
+a <I>template-declaration</I> declares exactly one entity
+(see <A HREF="2862.html">issue 2862</A>).</P>
+
+<P>As an aside, the paper as adopted misrepresents the status of
+members of dependent types, which are covered by
+13.7.5 [<A href="https://wg21.link/temp.friend#5">temp.friend</A>] paragraph 5.</P>
+
+<P>CWG welcomes a paper making the template friend cases valid, but
+such a facility would appear to require substantial changes to the
+normative wording, which a core issue is not equipped for.</P>
+
+<P>CWG asks EWG to consent to the reduction in scope for the variadic
+friends facility.</P>
+
 <BR><BR>
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