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    CWG Issue 2277</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="2277"></A><H4>2277.
  
Ambiguity inheriting constructors with default arguments
</H4>
<B>Section: </B>12.2.4.3&#160; [<A href="https://wg21.link/over.ics.rank">over.ics.rank</A>]
 &#160;&#160;&#160;

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

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

 <B>Date: </B>2016-06-23<BR>


<P>[Voted into the WP at the July, 2017 meeting.]</P>



<P>In an example like:</P>

<PRE>
  struct A {
    A(int, int = 0);
    void f(int, int = 0);
  };
  struct B : A {
    B(int); using A::A;
    void f(int); using A::f;
  }
</PRE>

<P>calls to <TT>B(int)</TT> and <TT>B::f(int)</TT> are ambiguous,
because they could equally call the version inherited from the
base class. This doesn't match the intent in
9.10 [<A href="https://wg21.link/namespace.udecl">namespace.udecl</A>], which usually makes derived-class
functions take precedence over ones from a base class.</P>

<P>The above patterns are not common, although they sometimes
cause breakage when refactoring a base class. However,
P0136R1 brings this into sharp focus, because it causes the
rejection of the following formerly-valid and very reasonable
code:</P>

<PRE>
  struct A {
    A(int = 0);
  };
  struct B : A {
    using B::B;
  };
  B b;
</PRE>

<P><B>Proposed resolution (May, 2017):</B></P>

<P>This issue is resolved by the resolution of
<A HREF="2273.html">issue 2273</A>.</P>

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