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    CWG Issue 2491</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="2491"></A><H4>2491.
  
Export of typedef after its first declaration
</H4>
<B>Section: </B>10.2&#160; [<A href="https://wg21.link/module.interface">module.interface</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD6
 &#160;&#160;&#160;

 <B>Submitter: </B>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2021-04-16<BR>


<P>[Accepted as a DR at the October, 2021 meeting.]</P>

<P>According to 10.2 [<A href="https://wg21.link/module.interface#6">module.interface</A>] paragraph 6,</P>

<BLOCKQUOTE>

<P>A redeclaration of an entity
or <I>typedef-name</I> <TT>X</TT> is implicitly exported if
<TT>X</TT> was introduced by an exported declaration;
otherwise it shall not be exported.  [<I>Example 4:</I>
</P>

<PRE>
  export module M;
  struct S { int n; };
  typedef S S;
  export typedef S S; //<SPAN CLASS="cmnt"> OK, does not redeclare an entity</SPAN>
  export struct S;    //<SPAN CLASS="cmnt"> error: exported declaration follows non-exported declaration</SPAN>
</PRE>

<P>&#8212;<I>end example</I>]</P>

</BLOCKQUOTE>

<P>The normative text says that exporting a typedef that was
not exported on its first declaration is ill-formed, but the
example does so and states that it is &#8220;OK&#8221;. This is a
contradiction that was introduced by the changes in paper
P1787R6; the previous normative text supported the usage in
the example.</P>

<P>(See also <A HREF="https://github.com/cplusplus/draft/issues/4540">
editorial issue 4540</A>.)</P>

<P><B>Proposed resolution, August, 2021:</B></P>

<P>Change 10.2 [<A href="https://wg21.link/module.interface#6">module.interface</A>] paragraph 6 as follows:</P>

<BLOCKQUOTE>

A redeclaration of an entity <DEL>or <I>typedef-name</I></DEL>
<TT>X</TT> is implicitly exported if <TT>X</TT> was
introduced by an exported declaration; otherwise it shall
not be exported.

</BLOCKQUOTE>

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