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    CWG Issue 331</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="331"></A><H4>331.
  
Allowed copy constructor signatures
</H4>
<B>Section: </B>11.4.5&#160; [<A href="https://wg21.link/class.ctor">class.ctor</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD1
 &#160;&#160;&#160;

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

 <B>Date: </B>8 Jan 2002<BR>


<P>[Voted into WP at October 2003 meeting.]</P>

<P>11.4.5 [<A href="https://wg21.link/class.ctor#10">class.ctor</A>] paragraph 10 states</P>
<BLOCKQUOTE>
A copy constructor for a class X is a constructor with a
first parameter of type X &amp; or of type const X &amp;.  [Note:
see 11.4.5.3 [<A href="https://wg21.link/class.copy.ctor">class.copy.ctor</A>] for more information on copy constructors.]
</BLOCKQUOTE>

<P>No mention is made of constructors with first parameters of types
volatile X &amp; or const volatile X &amp;.  This statement seems to be
in contradiction with 11.4.5.3 [<A href="https://wg21.link/class.copy.ctor#2">class.copy.ctor</A>] paragraph 2 which states</P>
<BLOCKQUOTE>
A non-template constructor for class X is a copy constructor
if its first parameter is of type X &amp;, const X &amp;, volatile X &amp;
or const volatile X &amp;, ...
</BLOCKQUOTE>

<P>11.4.5.3 [<A href="https://wg21.link/class.copy.ctor#5">class.copy.ctor</A>] paragraph 5 also mentions the volatile
versions of the
copy constructor, and the comparable paragraphs for copy assignment
(11.4.5.3 [<A href="https://wg21.link/class.copy.ctor">class.copy.ctor</A>] paragraphs 9 and 10) all allow volatile
versions, so it seems that 11.4.5 [<A href="https://wg21.link/class.ctor">class.ctor</A>] is at fault.</P>

<P><B>Proposed resolution (October 2002):</B></P>

<P>Change 11.4.5 [<A href="https://wg21.link/class.ctor#10">class.ctor</A>] paragraph 10 from
<BLOCKQUOTE>
A <I>copy constructor</I> for a class <TT>X</TT> is a constructor with a
first parameter of type <TT>X&amp;</TT> or of type <TT>const X&amp;</TT>.
[<I>Note:</I> see 11.4.5.3 [<A href="https://wg21.link/class.copy.ctor">class.copy.ctor</A>] for more information on
copy constructors. ]
</BLOCKQUOTE>
to (note that the dropping of italics is intentional):
<BLOCKQUOTE>
A copy constructor (11.4.5.3 [<A href="https://wg21.link/class.copy.ctor">class.copy.ctor</A>]) is used to copy objects
of class type.
</BLOCKQUOTE>
</P>

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