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    CWG Issue 2044</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="2044"></A><H4>2044.
  
<TT>decltype(auto)</TT> and <TT>void</TT>
</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>CD4
 &#160;&#160;&#160;

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

 <B>Date: </B>2014-11-14<BR>


<P>[Adopted at the February, 2016 meeting.]</P>



<P>The resolution of <A HREF="1877.html">issue 1877</A>
does not correctly
handle <TT>decltype(auto)</TT> return types with <TT>void</TT> return
expressions:</P>

<PRE>
  T f();
  decltype(auto) g() { return f(); }
</PRE>

<P>fails when <TT>T</TT> is <TT>void</TT>.</P>

<P><U>Suggested resolution:</U></P>

<P>Change 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#7">dcl.spec.auto</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

...In the case of a <TT>return</TT> with no operand or with an
operand of type <TT>void</TT>, the declared return type
shall be <TT>auto</TT> <INS>or <TT>decltype(auto)</TT></INS>
and the deduced return type is <TT>void</TT>. Otherwise...

</BLOCKQUOTE>

<P><B>Proposed resolution (September, 2015):</B></P>

<P>Change 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#7">dcl.spec.auto</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

<P>When a variable declared using a placeholder type is initialized, or a
<TT>return</TT> statement occurs in a function declared with a return type
that contains a placeholder type, the deduced return type or variable type
is determined from the type of its initializer. In the case of
a <TT>return</TT> with no operand or with an operand of type <TT>void</TT><DEL>,</DEL><INS>:</INS>
</P>

<UL>
<LI><P><INS>if the declared return type is <TT>decltype(auto)</TT>, then the
deduced return type is <TT>void</TT>;</INS></P></LI>

<LI><P>
<INS>otherwise, </INS>the declared return type shall
be <INS><I>cv</I></INS> <TT>auto</TT> and the deduced return type is
<INS><I>cv</I></INS> <TT>void</TT>.</P></LI>

</UL>

<P>Otherwise, let <TT>T</TT> be...</P>

</BLOCKQUOTE>

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