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    CWG Issue 2053</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="2053"></A><H4>2053.
  
<TT>auto</TT> in non-generic lambdas
</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>C++20
 &#160;&#160;&#160;

 <B>Submitter: </B>Faisal Vali
 &#160;&#160;&#160;

 <B>Date: </B>2014-12-07<BR>


<P>[Accepted as a DR at the February, 2020 (Prague) meeting.]</P>



<P>According to 9.2.9.7 [<A href="https://wg21.link/dcl.spec.auto#3">dcl.spec.auto</A>] paragraph 3,</P>

<BLOCKQUOTE>

If the <TT>auto</TT> <I>type-specifier</I> appears as one of
the <I>decl-specifier</I>s in the <I>decl-specifier-seq</I>
of a <I>parameter-declaration</I> of
a <I>lambda-expression</I>, the lambda is a <I>generic lambda</I>
(7.5.6 [<A href="https://wg21.link/expr.prim.lambda">expr.prim.lambda</A>]).

</BLOCKQUOTE>

<P>and 7.5.6 [<A href="https://wg21.link/expr.prim.lambda#5">expr.prim.lambda</A>] paragraph 5 says,

<BLOCKQUOTE>

For a generic lambda, the closure type has a public inline
function call operator member template
(13.7.3 [<A href="https://wg21.link/temp.mem">temp.mem</A>])
whose <I>template-parameter-list</I> consists of one
invented type <I>template-parameter</I> for each occurrence
of <TT>auto</TT> in the lambda's <I>parameter-declaration-clause</I>,
in order of appearance.

</BLOCKQUOTE>
</P>

<P>However, an <TT>auto</TT> that signals a
<I>trailing-return-type</I> should be excluded from these
descriptions.</P>

<P><B>Proposed resolution (February, 2020):</B></P>

<P>This issue is resolved by the resolution of
<A HREF="2447.html">issue 2447</A>.</P>

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