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    CWG Issue 2783</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="2783"></A><H4>2783.
  
Handling of deduction guides in <I>global-module-fragment</I>
</H4>
<B>Section: </B>10.4&#160; [<A href="https://wg21.link/module.global.frag">module.global.frag</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

 <B>Submitter: </B>Daniela Engert
 &#160;&#160;&#160;

 <B>Date: </B>2023-08-21<BR>


<P>[Accepted as a DR at the November, 2023 meeting.]</P>

<P>Consider:</P>

<PRE>
  // <SPAN CLASS="cmnt">header</SPAN> "S.h"
  
  template&lt;class T&gt;
  struct S {
    S(const T*);
  };
  template&lt;class T&gt;
  S(T*) -&gt; S&lt;T&gt;

  // <SPAN CLASS="cmnt">translation unit</SPAN>
  module;
  #include "S.h"

  export module M;
  export using ::S;
</PRE>

<P>Obviously, the <I>using-declaration</I> referring to the class
template <TT>S</TT> is exported by <TT>M</TT>, but what about the
deduction guide of <TT>S</TT>?</P>

<P><B>Proposed resolution (approved by CWG 2023-08-25) [SUPERSEDED]:</B></P>

<P>Add a new bullet after 10.4 [<A href="https://wg21.link/module.global.frag#3.5.7">module.global.frag</A>] bullet 3.5.7 as
follows:</P>

<BLOCKQUOTE>

<UL>
<LI>...</LI>
<LI>
there exists a declaration M that is not a <I>namespace-definition</I>
for which M is decl-reachable from S and either
<UL>
<LI>...</LI>
<LI>one of M and D declares a template and the other declares a
partial or explicit specialization or an implicit or explicit
instantiation of that template, or</LI>
<LI class="ins">one of M and D declares a class template and the other
declares a deduction guide for that template, or</LI>
</UL>
</LI>
</UL>

</BLOCKQUOTE>

<P><B>Proposed resolution (approved by CWG 2023-10-06):</B></P>

<P>Add a new bullet after 10.4 [<A href="https://wg21.link/module.global.frag#3.5.7">module.global.frag</A>] bullet 3.5.7 as
follows:</P>

<BLOCKQUOTE>

<UL>
<LI>...</LI>
<LI>
there exists a declaration M that is not a <I>namespace-definition</I>
for which M is decl-reachable from S and either
<UL>
<LI>...</LI>
<LI>one of M and D declares a template and the other declares a
partial or explicit specialization or an implicit or explicit
instantiation of that template, or</LI>
<LI class="ins">M declares a class template and D
is a deduction guide for that template, or</LI>
</UL>
</LI>
</UL>

</BLOCKQUOTE>

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