<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 984</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="984"></A><H4>984.
  
&#8220;Deduced type&#8221; is unclear in <TT>auto</TT> type deduction
</H4>
<B>Section: </B>9.2.9.7&#160; [<A href="https://wg21.link/dcl.spec.auto">dcl.spec.auto</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Michael Wong
 &#160;&#160;&#160;

 <B>Date: </B>19 October, 2009<BR>


<P>[Voted into WP at March, 2010 meeting.]</P>

<P>9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#6">dcl.spec.auto</A>] paragraph 6 says,</P>

<BLOCKQUOTE>

Once the type of a <I>declarator-id</I> has been determined according
to 9.3.4 [<A href="https://wg21.link/dcl.meaning">dcl.meaning</A>], the type of the declared variable using
the <I>declarator-id</I> is determined from the type of its
initializer using the rules for template argument deduction.  Let
<TT>T</TT> be the type that has been determined for a variable
identifier <TT>d</TT>.  Obtain <TT>P</TT> from <TT>T</TT> by replacing
the occurrences of <TT>auto</TT> with either a new invented type
template parameter <TT>U</TT> or, if the initializer is a
<I>braced-init-list</I> (9.5.5 [<A href="https://wg21.link/dcl.init.list">dcl.init.list</A>]), with
<TT>std::initializer_list&lt;U&gt;</TT>.  The type deduced for the
variable <TT>d</TT> is then the deduced type determined using the
rules of template argument deduction from a function call
(13.10.3.2 [<A href="https://wg21.link/temp.deduct.call">temp.deduct.call</A>]), where <TT>P</TT> is a function
template parameter type and the initializer for <TT>d</TT> is the
corresponding argument.

</BLOCKQUOTE>

<P>The reference to &#8220;the deduced type&#8221; is unclear; it
could be taken as referring either to the template parameter or to the
function parameter type.  13.10.3.2 [<A href="https://wg21.link/temp.deduct.call">temp.deduct.call</A>] uses the term
&#8220;deduced <TT>A</TT>,&#8221; and that usage should be repeated
here.</P>

<P><B>Proposed resolution (October, 2009):</B></P>

<P>Change 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#6">dcl.spec.auto</A>] paragraph 6 as follows:</P>

<BLOCKQUOTE>

...The type deduced for the variable <TT>d</TT> is then the deduced
<DEL>type</DEL> <INS><TT>A</TT></INS> determined using the rules of
template argument deduction...

</BLOCKQUOTE>

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