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    CWG Issue 1942</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="1942"></A><H4>1942.
  
Incorrect reference to <I>trailing-return-type</I>
</H4>
<B>Section: </B>7.5.6&#160; [<A href="https://wg21.link/expr.prim.lambda">expr.prim.lambda</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

 <B>Submitter: </B>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>2014-06-16<BR>


<P>[Moved to DR at the May, 2015 meeting.]</P>

<P>According to 7.5.6 [<A href="https://wg21.link/expr.prim.lambda#4">expr.prim.lambda</A>] paragraph 4,</P>

<BLOCKQUOTE>

If a <I>lambda-expression</I> does not include
a <I>lambda-declarator</I>, it is as if
the <I>lambda-declarator</I> were <TT>()</TT>. The lambda return
type is <TT>auto</TT>, which is replaced by
the <I>trailing-return-type</I> if provided...

</BLOCKQUOTE>

<P>
<I>trailing-return-type</I> is a syntactic nonterminal that
includes the <TT>-&gt;</TT> and thus cannot be used directly to
refer to the type.  It should instead say something like, ...the
type specified by the <I>trailing-return-type</I>.</P>

<P>The reference in 9.3.4.6 [<A href="https://wg21.link/dcl.fct#2">dcl.fct</A>] paragraph 2,
 &#8220;...returning
<I>trailing-return-type</I>&#8221; should be similarly adjusted.</P>

<P><B>Proposed resolution (November, 2014):</B></P>

<OL>
<LI><P>Change 7.5.6 [<A href="https://wg21.link/expr.prim.lambda#4">expr.prim.lambda</A>] paragraph 4 as follows:</P></LI>

<BLOCKQUOTE>

If a <I>lambda-expression</I> does not include
a <I>lambda-declarator</I>, it is as if
the <I>lambda-declarator</I> were <TT>()</TT>. The lambda return type
is <TT>auto</TT>, which is replaced by <INS>the type specified by</INS>
the <I>trailing-return-type</I> if provided and/or deduced
from <TT>return</TT> statements as described in
9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto">dcl.spec.auto</A>]. [<I>Example:</I>...

</BLOCKQUOTE>

<LI><P>Change 9.3.4.6 [<A href="https://wg21.link/dcl.fct#2">dcl.fct</A>] paragraph 2 as follows:</P></LI>

<BLOCKQUOTE>

The type of the <I>declarator-id</I> in <TT>D</TT> is
&#8220;<I>derived-declarator-type-list</I> function of
(<I>parameter-declaration-clause</I>) <I>cv-qualifier-seq<SUB>opt</SUB></I>
<I>ref-qualifier<SUB>opt</SUB></I>
returning <DEL><I>trailing-return-type</I></DEL>
<INS><TT>U</TT></INS>&#8221;<INS>,
where <TT>U</TT> is the type specified by the
<I>trailing-return-type</I></INS>.  The
optional <I>attribute-specifier-seq</I>...

</BLOCKQUOTE>

</OL>

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