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    CWG Issue 850</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="850"></A><H4>850.
  
Restrictions on use of non-static data members
</H4>
<B>Section: </B>_N4567_.5.1.1&#160; [<A href="https://wg21.link/expr.prim.general">expr.prim.general</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Jason Merrill
 &#160;&#160;&#160;

 <B>Date: </B>1 April, 2009<BR>


<P>[Voted into WP at October, 2009 meeting.]</P>



<P>The resolution of <A HREF="613.html">issue 613</A>, as
reflected in the sixth bullet of _N4567_.5.1.1 [<A href="https://wg21.link/expr.prim.general">expr.prim.general</A>] paragraph
10, allows an <I>id-expression</I> designating a non-static data member
to be used</P>

<BLOCKQUOTE>

<UL><LI>if... it is the sole constituent of an unevaluated operand,
except for optional enclosing parentheses.</LI></UL>

</BLOCKQUOTE>

<P>The requirement that the <I>id-expression</I> be the &#8220;sole
constituent&#8221; of the unevaluated operand seems unnecessarily
strict, forbidding such plausible use cases as</P>

<PRE>
    struct S {
        int ar[42];
    };
    int i = sizeof(S::ar[0]);
</PRE>

<P>or the use of the member as a function argument in template
metaprogramming.  The more general version of the restriction seems
not to be very difficult to implement and may actually represent a
simplification in some implementations.</P>

<P><B>Proposed resolution (July, 2009):</B></P>

<P>Change _N4567_.5.1.1 [<A href="https://wg21.link/expr.prim.general#10">expr.prim.general</A>] paragraph 10 as follows:</P>

<UL>
<LI><P>...</P></LI>

<LI>
<P>if that <I>id-expression</I> denotes a non-static data member
and it <DEL>is the sole constituent of</DEL> <INS>appears in</INS> an
unevaluated operand<DEL>, except for optional enclosing
parentheses</DEL>. [<I>Example:</I>
</P>

<PRE>
  struct S {
    int m;
  };
  int i = sizeof(S::m);        //<SPAN CLASS="cmnt"> OK</SPAN>
  int j = sizeof(S::m + 42);   //<SPAN CLASS="cmnt"> <DEL>error: reference to non-static member in subexpression</DEL> <INS>OK</INS></SPAN>
</PRE>

<P>&#8212;<I>end example</I>]</P>

</LI>

</UL>

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