<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1614</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<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="1614"></A><H4>1614.
  
Address of pure virtual function vs odr-use
</H4>
<B>Section: </B>6.3&#160; [<A href="https://wg21.link/basic.def.odr">basic.def.odr</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

 <B>Submitter: </B>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2013-01-31<BR>


<P>[Moved to DR at the November, 2014 meeting.]</P>

<P>According to 6.3 [<A href="https://wg21.link/basic.def.odr#3">basic.def.odr</A>] paragraph 3,</P>

<BLOCKQUOTE>

A function whose name appears as a potentially-evaluated expression is
odr-used if it is the unique lookup result or the selected member of a set
of overloaded functions (6.5 [<A href="https://wg21.link/basic.lookup">basic.lookup</A>],
12.2 [<A href="https://wg21.link/over.match">over.match</A>], 12.3 [<A href="https://wg21.link/over.over">over.over</A>]), unless it is a pure
virtual function and its name is not explicitly qualified.

</BLOCKQUOTE>

<P>In the following example, consequently, <TT>S::f</TT> is odr-used but
not defined, and (because it is an undefined odr-used inline function) a
diagnostic is required:</P>

<PRE>
  namespace {
    struct S {
      inline virtual void f() = 0;
    };
   void (S::*p) = &amp;S::f;
  }
</PRE>

<P>However, <TT>S::f</TT> cannot be called through such a
pointer-to-member, so forming a pointer-to-member should not
cause a pure virtual function to be odr-used.  There is
implementation divergence on this point.</P>

<P><B>Proposed resolution (April, 2013):</B></P>

<P>Change 6.3 [<A href="https://wg21.link/basic.def.odr#3">basic.def.odr</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

...A virtual member function is odr-used if it is not pure. A function
whose name appears as a potentially-evaluated expression is odr-used if it
is the unique lookup result or the selected member of a set of overloaded
functions (6.5 [<A href="https://wg21.link/basic.lookup">basic.lookup</A>], 12.2 [<A href="https://wg21.link/over.match">over.match</A>],
12.3 [<A href="https://wg21.link/over.over">over.over</A>]), unless it is a pure virtual function and
<INS>either</INS> its name is not explicitly qualified <INS>or the
expression forms a pointer to member (5.3.1)</INS>. [<I>Note:</I>...

</BLOCKQUOTE>

<BR><BR>
</BODY>
</HTML>
