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    CWG Issue 2360</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="2360"></A><H4>2360.
  
<TT>[[maybe_unused]]</TT> and structured bindings
</H4>
<B>Section: </B>9.13.8&#160; [<A href="https://wg21.link/dcl.attr.unused">dcl.attr.unused</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD5
 &#160;&#160;&#160;

 <B>Submitter: </B>Michael Wong
 &#160;&#160;&#160;

 <B>Date: </B>2017-10-19<BR>


<P>[Accepted as a DR at the February, 2019 meeting.]</P>

<P>According to9.13.8 [<A href="https://wg21.link/dcl.attr.unused#2">dcl.attr.unused</A>] paragraph 2,</P>

<BLOCKQUOTE>

The attribute may be applied to the declaration of a class,
a <I>typedef-name</I>, a variable, a non-static data member, a function, an
enumeration, or an enumerator.

</BLOCKQUOTE>

<P>This does not include structured bindings, although there seems to be
no good reason to prohibit uses like</P>

<PRE>
  [[maybe_unused]] auto [a, b] = std::make_pair(42, 0.23);
</PRE>

<P><B>Notes from the October, 2018 teleconference:</B></P>

<P>CWG agreed that such an annotation should be permitted and apply
to the underlying variable; i.e., a compiler might warn in the absence
of such an attribute if none of the structured bindings were used, and
the presence of the attribute would silence such warnings.</P>

<P><B>Proposed resolution (November, 2018):</B></P>

<P>Change 9.13.8 [<A href="https://wg21.link/dcl.attr.unused">dcl.attr.unused</A>] paragraphs 2 and 3 as
follows:</P>

<BLOCKQUOTE>

<P>The attribute may be applied to the declaration of a class,
a <I>typedef-name</I>, a variable <INS>(including a structured
binding declaration)</INS>, a non-static data member,
a function, an enumeration, or an enumerator.</P>

<P>
<DEL>[<I>Note:</I></DEL> For an entity
marked <TT>maybe_unused</TT>, implementations should not
emit a warning that the entity <DEL>is</DEL>
<INS>or its structured bindings
(if any) are used or</INS>
unused<INS>.</INS>
<DEL>, or that the entity
is used despite the presence of the attribute. &#8212;<I>end
note</I>]</DEL> <INS>For a structured binding declaration
not marked <TT>maybe_unused</TT>, implementations should not
emit such a warning unless all of its structured bindings are
unused.</INS>
</P>

</BLOCKQUOTE>

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