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    CWG Issue 1437</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="1437"></A><H4>1437.
  
<TT>alignas</TT> in <I>alias-declaration</I>
</H4>
<B>Section: </B>9.2.4&#160; [<A href="https://wg21.link/dcl.typedef">dcl.typedef</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD3
 &#160;&#160;&#160;

 <B>Submitter: </B>Daveed Vandevoorde
 &#160;&#160;&#160;

 <B>Date: </B>2012-01-02<BR>


<P>[Moved to DR at the April, 2013 meeting.]</P>

<P>Consider the following:</P>

<PRE>
    struct S { int i; };
    using A alignas(alignof(long long)) = S;
</PRE>

<P>9.13.2 [<A href="https://wg21.link/dcl.align#1">dcl.align</A>] paragraph 1 allows an <I>alignment-specifier</I>
to be applied to the declaration of a class or enumeration type, which
<TT>A</TT> arguably is.  The specification should be clarified to indicate
that such a usage is not permitted, however.</P>

<P><B>Proposed resolution (October, 2012):</B></P>

<P>Change 9.13.2 [<A href="https://wg21.link/dcl.align#1">dcl.align</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

An <I>alignment-specifier</I> may be applied to a variable or to a
class data member, but it shall not be applied to a bit-field, a
function parameter, <DEL>the formal parameter of a catch clause</DEL>
<INS>an <I>exception-declaration</I></INS> (14.4 [<A href="https://wg21.link/except.handle">except.handle</A>]), or a variable declared with the <TT>register</TT>
storage class specifier. An <I>alignment-specifier</I> may also be
applied to the declaration <DEL>of a class or enumeration type</DEL>
<INS>or definition of a class (in an <I>elaborated-type-specifier</I>
(9.2.9.5 [<A href="https://wg21.link/dcl.type.elab">dcl.type.elab</A>]) or <I>class-head</I> (
Clause 11 [<A href="https://wg21.link/class">class</A>]), respectively) and to the declaration or
definition of an enumeration (in an <I>opaque-enum-declaration</I> or
<I>enum-head</I>, respectively (9.8.1 [<A href="https://wg21.link/dcl.enum">dcl.enum</A>]))</INS>. An
<I>alignment-specifier</I> with an ellipsis is a pack expansion
(13.7.4 [<A href="https://wg21.link/temp.variadic">temp.variadic</A>]).

</BLOCKQUOTE>

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