<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 2714</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<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="2714"></A><H4>2714.
  
Implicit deduction guides omit properties from the parameter-declaration-clause of a constructor
</H4>
<B>Section: </B>12.2.2.9&#160; [<A href="https://wg21.link/over.match.class.deduct">over.match.class.deduct</A>]
 &#160;&#160;&#160;

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

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

 <B>Date: </B>2017-02-13<BR>


<P>[Accepted as a DR at the March, 2024 meeting.]</P>



<P>Subclause 12.2.2.9 [<A href="https://wg21.link/over.match.class.deduct#1.1.2">over.match.class.deduct</A>] bullet 1.1.2 specifies:</P>

<BLOCKQUOTE>

<UL>
<LI>The types of the function parameters are those of the constructor.
</LI>
</UL>

</BLOCKQUOTE>

<P>However, this does not consider default arguments or variadic
constructors.</P>

<P><B>Proposed resolution (approved by CWG 2023-04-28):</B></P>

<P>(This also resolves <A HREF="2628.html">issue 2628</A>.)</P>

<P>Change in 12.2.2.9 [<A href="https://wg21.link/over.match.class.deduct#1">over.match.class.deduct</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

<UL>
<LI>If C is defined, for each constructor of C, a function template with
the following properties:
<UL>
<LI>The template parameters are the
template parameters of C followed by the template parameters
(including default template arguments) of the constructor, if any.
</LI>
<LI>
<INS>The associated constraints (13.5.3 [<A href="https://wg21.link/temp.constr.decl">temp.constr.decl</A>]) are
the conjunction of the associated constraints of <TT>C</TT> and the associated
constraints of the constructor, if any. [ Note: A
<I>constraint-expression</I> in the <I>template-head</I> of <TT>C</TT>
is checked for satisfaction before any constraints from the
<I>template-head</I> or <I>trailing-requires-clause</I> of the
constructor. -- end note ]</INS>
</LI>
<LI>The <DEL>types of the function parameters are those</DEL>
<INS><I>parameter-declaration-clause</I> is that</INS> of the
constructor.
</LI>
<LI>The return type is the class template
specialization designated by C and template arguments corresponding to
the template parameters of C.
</LI>
</UL>
</LI>
<LI>If C is not defined or does not
declare any constructors, an additional function template derived as
above from a hypothetical constructor C().</LI>
<LI>An additional
function template derived as above from a hypothetical constructor
C(C), called the copy deduction candidate.</LI>
<LI>For each <I>deduction-guide</I>, a function or function template
with the following properties:
<UL>
<LI>The <DEL>template
parameters</DEL> <INS><I>template-head</I></INS>, if any, and
<DEL>function parameters</DEL>
<INS><I>parameter-declaration-clause</I></INS> are those of
the <I>deduction-guide</I>.
</LI>
<LI>The return type is the <I>simple-template-id</I> of
the <I>deduction-guide</I>.
</LI>
</UL>
</LI>
</UL>
</BLOCKQUOTE>

<BR><BR>
</BODY>
</HTML>
