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    CWG Issue 927</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="927"></A><H4>927.
  
Implicitly-deleted default constructors and member initializers
</H4>
<B>Section: </B>11.4.5&#160; [<A href="https://wg21.link/class.ctor">class.ctor</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Alisdair Meredith
 &#160;&#160;&#160;

 <B>Date: </B>1 July, 2009<BR>


<P>[Voted into WP at March, 2010 meeting.]</P>

<commmittee_only><P>(From message <A href="http://listarchives.isocpp.org/cgi-bin/wg21/message?wg=core&amp;msg=14555">14555</A>.)</P></commmittee_only>

<P>The reasons for which an implicitly-declared default constructor is
defined as deleted, given in 11.4.5 [<A href="https://wg21.link/class.ctor#4">class.ctor</A>] paragraph 4,
all deal with cases in which a member cannot be
default-initialized. Presumably a <I>brace-or-equal-initializer</I>
for such a member would eliminate the need to define the constructor
as deleted, but this case is not addressed by the current wording.</P>

<P><B>Proposed resolution (October, 2009):</B></P>

<P>Change 11.4.5 [<A href="https://wg21.link/class.ctor#5">class.ctor</A>] paragraph 5, the second list, as
follows:</P>

<BLOCKQUOTE>

<P>An implicitly-declared default constructor for class <TT>X</TT> is
defined as deleted if:</P>

<UL>
<LI><P>
<TT>X</TT> is a union-like class that has a variant member
with a non-trivial default constructor,</P></LI>

<LI><P>any non-static data member <INS>with no
<I>brace-or-equal-initializer</I></INS> is of reference type,</P></LI>

<LI><P>any non-static data member of const-qualified type (or array
thereof) <INS>with no <I>brace-or-equal-initializer</I></INS> does not
have a user-provided default constructor, or</P></LI>

<LI><P>any <INS>direct or virtual base class, or</INS> non-static data
member <INS>with no <I>brace-or-qual-initializer,</I></INS> <DEL>or
direct or virtual base class</DEL> has class type <TT>M</TT> (or array
thereof) and <INS>either</INS> <TT>M</TT> has no default
<DEL>constructor, or if</DEL> <INS>constructor or</INS> overload
resolution (12.2 [<A href="https://wg21.link/over.match">over.match</A>]) as applied to <TT>M</TT>'s
default constructor<DEL>,</DEL> results in an ambiguity or
<INS>in</INS> a function that is deleted or inaccessible from the
implicitly-declared default constructor.</P></LI>

</UL>

</BLOCKQUOTE>

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