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    CWG Issue 2795</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="2795"></A><H4>2795.
  
Overlapping empty subobjects with different cv-qualification
</H4>
<B>Section: </B>6.8.2&#160; [<A href="https://wg21.link/intro.object">intro.object</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

 <B>Submitter: </B>Jonathan Caves
 &#160;&#160;&#160;

 <B>Date: </B>2023-09-04<BR>


<P>[Accepted as a DR at the November, 2023 meeting.]</P>



<P>Subclause 6.8.2 [<A href="https://wg21.link/intro.object#9">intro.object</A>] paragraph 9 specifies:</P>

<BLOCKQUOTE>

... Two objects with overlapping lifetimes that are not bit-fields may
have the same address if one is nested within the other, or if at
least one is a subobject of zero size and they are of different types;
otherwise, they have distinct addresses and occupy disjoint bytes of
storage. [ Footnote: ... ]

</BLOCKQUOTE>

<P>Types <TT>T</TT> and <TT>const T</TT> are different types, but it
is unlikely the rule is intending to differentiate along that
line.</P>

<P><U>Suggested resolution [SUPERSEDED]:</U></P>

<P>Change in 6.8.2 [<A href="https://wg21.link/intro.object#9">intro.object</A>] paragraph 9 as follows:</P>

<BLOCKQUOTE>

... Two objects with overlapping lifetimes that are not bit-fields may
have the same address if one is nested within the other, or if at
least one is a subobject of zero size and they are of different types
<INS>(ignoring top-level cv-qualifiers)</INS>; otherwise, they have
distinct addresses and occupy disjoint bytes of storage. [ Footnote:
... ]

</BLOCKQUOTE>

<P><B>Proposed resolution (approved by CWG 2023-09-15):</B></P>

<P>(Hypothetically, pointer-to-member types can be empty, but might
differ in non-top-level cv-qualification.)</P>

<P>Change in 6.8.2 [<A href="https://wg21.link/intro.object#9">intro.object</A>] paragraph 9 as follows:</P>

<BLOCKQUOTE>

... Two objects with overlapping lifetimes that are not bit-fields may
have the same address if one is nested within the other, or if at
least one is a subobject of zero size and they are <INS>not</INS>
of <DEL>different</DEL> <INS>similar</INS>
types <INS>(7.3.6 [<A href="https://wg21.link/conv.qual">conv.qual</A>])</INS>; otherwise, they have
distinct addresses and occupy disjoint bytes of storage. [ Footnote:
... ]

</BLOCKQUOTE>

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