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    CWG Issue 1941</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="1941"></A><H4>1941.
  
SFINAE and inherited constructor default arguments
</H4>
<B>Section: </B>_N4527_.12.9&#160; [<A href="https://wg21.link/class.inhctor">class.inhctor</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>David Krauss
 &#160;&#160;&#160;

 <B>Date: </B>2014-06-12<BR>


<P>[Adopted at the October, 2015 meeting as P0136R1.]</P>

<P>Default arguments are a common mechanism for applying SFINAE to
constructors.  However, default arguments are not carried over
when base class constructors are inherited; instead, an overload
set of constructors with various numbers of arguments is created
in the derived class.  This seems problematic.</P>

<P>One possibility would be to change the mechanism for how
constructors are inherited; a <I>using-declaration</I> might
actually introduce the base class constructors into the derived
class, as other <I>using-declaration</I>s do, and if a base class
constructor were selected, the remaining derived class members
would be default-initialized.</P>

<P>This approach would also address issues <A HREF="1645.html">1645</A>, as duplicated constructors would simply fail during
overload resolution, and <A HREF="1715.html">1715</A>, since
there would be no synthesized constructors for which access
checking would be needed.</P>

<P>The effect of such an approach on ABIs, including mangling, would
need to be considered.</P>

<P>See also <A HREF="1959.html">issue 1959</A>.</P>

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