<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 360</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="360"></A><H4>360.
  
Using-declaration that reduces access
</H4>
<B>Section: </B>11.8.3&#160; [<A href="https://wg21.link/class.access.base">class.access.base</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD6
 &#160;&#160;&#160;

 <B>Submitter: </B>Steve Clamage
 &#160;&#160;&#160;

 <B>Date: </B>4 June 2002<BR>


<P>[Accepted at the November, 2020 meeting as part of paper P1787R6 and
moved to DR at the February, 2021 meeting.]</P>



<P>I have heard a claim that the following code is valid, but I don't
see why.</P>
<PRE>
  struct A {
    int foo ();
  };

  struct B: A {
  private:
    using A::foo;
  };

  int main ()
  {
    return B ().foo ();
  }
</PRE>
<P>
It seems to me that the using declaration in B should hide the
public foo in A. Then the call to B::foo should fail because B::foo
is not accessible in main.</P>

<P>Am I missing something?</P>

<P>
<U>Steve Adamczyk</U>:
This is similar to the last example in 11.8.3 [<A href="https://wg21.link/class.access.base">class.access.base</A>].
In prose, the rule is
that if you have access to cast to a base class and you have access
to the member in the base class, you are given access in the derived
class.  In this case, A is a public base class of B and foo is public
in A, so you can access foo through a B object.  The actual permission
for this is in the fourth bullet in
11.8.3 [<A href="https://wg21.link/class.access.base#4">class.access.base</A>] paragraph 4.</P>

<P>The wording changes for <A HREF="9.html">issue 9</A>
make this clearer, but I believe
even without them this example could be discerned to be valid.</P>

<P>See my paper J16/96-0034, WG21/N0852 on this topic.</P>

<P>
<U>Steve Clamage</U>:
But a using-declaration is a declaration (9.10 [<A href="https://wg21.link/namespace.udecl">namespace.udecl</A>]).
Compare with</P>
<PRE>
  struct B : A {
  private:
    int foo();
  };
</PRE>
<P>In this case, the call would certainly be invalid, even though your
argument about casting B to an A would make it OK. Your argument
basically says that an access adjustment to make something less
accessible has no effect. That also doesn't sound right.</P>

<P>
<U>Steve Adamczyk</U>:
I agree that is strange.  I do think that's what 11.8.3 [<A href="https://wg21.link/class.access.base">class.access.base</A>]
says, but perhaps that's not what we want it to say.</P>

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