<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 711</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="711"></A><H4>711.
  
<TT>auto</TT> with <I>braced-init-list</I>
</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>Jason Merrill
 &#160;&#160;&#160;

 <B>Date: </B>27 August, 2008<BR>


<P>[Voted into WP at July, 2009 meeting.]</P>



<P>One effect of the initializer-list proposal is that now we
allow</P>

<PRE>
    auto x = { 1, 2, 3 };  //<SPAN CLASS="cmnt"> </SPAN>decltype(x)<SPAN CLASS="cmnt"> is </SPAN>std::initializer_list&lt;int&gt;
</PRE>

<P>but not</P>

<PRE>
    auto ar[3] = { 1, 2, 3 };  //<SPAN CLASS="cmnt"> ill-formed</SPAN>
</PRE>

<P>This seems unfortunate, as the code for the first could also
support the second.  Incidentally, I also failed to update the
text in 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#3">dcl.spec.auto</A>] paragraph 3 which forbids
the use of <TT>auto</TT> with <I>braced-init-list</I>s, so
technically the first form above is currently ill-formed but has
defined semantics.
</P>

<P>
<U>Bjarne Stroustrup</U>:</P>

<P>Is this the thin edge of a wedge? How about</P>

<PRE>
    vector&lt;auto&gt; v = { 1, 2, 3 };
</PRE>

<P>and</P>

<PRE>
    template&lt;class T&gt; void f(vector&lt;T&gt;&amp; v);
    f({1, 2, 3 });
</PRE>

<P>(See also <A HREF="625.html">issue 625</A>.)</P>

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

<P>Change 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#3">dcl.spec.auto</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

...The <I>decl-specifier-seq</I> shall be followed by one or more
<I>init-declarator</I>s, each of which shall have a non-empty
<I>initializer</I><INS>.</INS> <DEL>of either of the following forms:

<UL>
<TT>=</TT> <I>assignment-expression</I><BR>
<TT>(</TT> <I>assignment-expression</I> <TT>)</TT>
</UL></DEL>

</BLOCKQUOTE>

<P><I>[Drafting note: This change does not address the original
issue of the inability to use <TT>auto</TT> with an array initializer,
only the secondary issue of permitted the braced-init-list.  The
CWG explicitly decided not to support the array case.]</I></P>

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