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    CWG Issue 2422</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="2422"></A><H4>2422.
  
Incorrect grammar for <I>deduction-guide</I>
</H4>
<B>Section: </B>13.7.2.3&#160; [<A href="https://wg21.link/temp.deduct.guide">temp.deduct.guide</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++20
 &#160;&#160;&#160;

 <B>Submitter: </B>Barry Revzin
 &#160;&#160;&#160;

 <B>Date: </B>2019-07-28<BR>


<P>[Adopted as a DR at the November, 2019 meeting.]</P>

<P>According to 13.7.2.3 [<A href="https://wg21.link/temp.deduct.guide#1">temp.deduct.guide</A>] paragraph 1, the syntax of
a <I>deduction-guide</I> is:</P>

<UL>
<I>deduction-guide:</I>
<UL>
<TT>explicit</TT><I><SUB>opt</SUB> template-name</I> <TT>(</TT><I> parameter-declaration-clause</I> <TT>) -&gt;</TT> <I>simple-template-id</I> <TT>;</TT>
</UL>
</UL>

<P>Instead of <TT>explicit</TT>, this production should use the
<I>explicit-specifier</I> nonterminal. (The wording of
12.2.2.9 [<A href="https://wg21.link/over.match.class.deduct">over.match.class.deduct</A>] has references to the
<I>explicit-specifier</I> of a deduction guide, for example.)</P>

<P><B>Proposed resolution (September, 2019):</B></P>

<P>Change the grammar in 13.7.2.3 [<A href="https://wg21.link/temp.deduct.guide#1">temp.deduct.guide</A>] paragraph 1 as
follows:</P>

<UL>
<I>deduction-guide:</I>
<UL>
<DEL><TT>explicit</TT></DEL>
<INS><I>explicit-specifier</I></INS><I><SUB>opt</SUB> template-name </I><TT>(</TT><I> parameter-declaration-clause </I><TT>) -&gt;</TT><I> simple-template-id </I><TT>;</TT>
</UL>
</UL>

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