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    CWG Issue 1567</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="1567"></A><H4>1567.
  
Inheriting constructors and copy/move constructors
</H4>
<B>Section: </B>_N4527_.12.9&#160; [<A href="https://wg21.link/class.inhctor">class.inhctor</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++14
 &#160;&#160;&#160;

 <B>Submitter: </B>Jason Merrill
 &#160;&#160;&#160;

 <B>Date: </B>2012-10-10<BR>


<P>[Moved to DR at the September, 2013 meeting.]</P>



<P>According to _N4527_.12.9 [<A href="https://wg21.link/class.inhctor#3">class.inhctor</A>] paragraph 3,</P>

<BLOCKQUOTE>

For each non-template constructor in the candidate set of inherited
constructors other than a constructor having no parameters or a
copy/move constructor having a single parameter, a constructor is
implicitly declared with the same constructor characteristics unless
there is a user-declared constructor with the same signature in the
class where the <I>using-declaration</I> appears.

</BLOCKQUOTE>

<P>It seems that this should be suppressing constructors that would
be copy/move constructors in the derived class rather than copy/move
constructors in the base class.  For example:</P>

<PRE>
  struct B;
  struct A {
    A(const A&amp;);
    A(const B&amp;);
    A(int);
  };

  struct B: A {
    using A::A;
  };
</PRE>

<P>If <TT>B::B(const B&amp;)</TT> is an inheriting constructor, other
subobjects of <TT>B</TT> will not be copied.  Also, if
<TT>A::A(const A&amp;)</TT> is not inherited, <TT>B</TT> objects
cannot be constructed from an <TT>A</TT> object.</P>

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

<P>Change _N4527_.12.9 [<A href="https://wg21.link/class.inhctor#3">class.inhctor</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

For each non-template constructor in the candidate set of inherited
constructors other than a constructor having no parameters or a
copy/move constructor having a single parameter, a constructor is
implicitly declared with the same constructor characteristics unless
there is a user-declared constructor with the same signature in the
class where the <I>using-declaration</I> appears <INS>or the
constructor would be a default, copy, or move constructor for that
class</INS>.

</BLOCKQUOTE>

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