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    CWG Issue 2356</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="2356"></A><H4>2356.
  
Base class copy and move constructors should not be inherited
</H4>
<B>Section: </B>12.2.2&#160; [<A href="https://wg21.link/over.match.funcs">over.match.funcs</A>]
 &#160;&#160;&#160;

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

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

 <B>Date: </B>2018-02-26<BR>


<P>[Accepted as a DR at the June, 2018 (Rapperswil) meeting.]</P>

<P>Base class copy and move constructors brought into a derived class via a
<I>using-declaration</I> should not be considered by overload resolution
when constructing a derived class object.</P>

<P><B>Proposed resolution, February, 2018:</B></P>

<P>Change 12.2.2 [<A href="https://wg21.link/over.match.funcs#8">over.match.funcs</A>] paragraph 8 as follows:</P>

<BLOCKQUOTE>

<P>A defaulted move special function (11.4.5.3 [<A href="https://wg21.link/class.copy.ctor">class.copy.ctor</A>]) that is
defined as deleted is excluded from the set of candidate functions in all
contexts. <INS>A constructor inherited from class type <TT>C</TT>
(11.9.4 [<A href="https://wg21.link/class.inhctor.init">class.inhctor.init</A>]) that has a first parameter of type
&#8220;reference to <I>cv1</I> <TT>P</TT>&#8221; (including such a
constructor instantiated from a template) is excluded from the set of
candidate functions when constructing an object of type <I>cv2</I>
<TT>D</TT> if the argument list has exactly one argument and <TT>C</TT>
is reference-related to <TT>P</TT> and <TT>P</TT> is reference-related
to <TT>D</TT>. [<I>Example:</I></INS>
</P>

<PRE>
<INS>  struct A {
    A();
    A(A &amp;&amp;);                        //<SPAN CLASS="cmnt"> #1</SPAN>
    template&lt;typename T&gt; A(T &amp;&amp;);   //<SPAN CLASS="cmnt"> #2</SPAN>
  };
  struct B : A {
    using A::A;
    B(const B &amp;);                   //<SPAN CLASS="cmnt"> #3</SPAN>
    B(B &amp;&amp;) = default;              //<SPAN CLASS="cmnt"> #4, implicitly deleted</SPAN>

    struct X { X(X &amp;&amp;) = delete; } x;
  };
  extern B b1;
  B b2 = static_cast&lt;B&amp;&amp;&gt;(b1);      //<SPAN CLASS="cmnt"> calls #3: #1, #2, and #4 are not viable</SPAN>
  struct C { operator B&amp;&amp;(); };
  B b3 = C();                       //<SPAN CLASS="cmnt"> calls #3</SPAN></INS>
</PRE>

<P><INS>&#8212;<I>end example</I>]</INS></P>

</BLOCKQUOTE>

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