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    CWG Issue 1409</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="1409"></A><H4>1409.
  
What is the second standard conversion sequence of a list-initialization sequence?
</H4>
<B>Section: </B>12.2.4.2.6&#160; [<A href="https://wg21.link/over.ics.list">over.ics.list</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD3
 &#160;&#160;&#160;

 <B>Submitter: </B>Sebastian Redl
 &#160;&#160;&#160;

 <B>Date: </B>2011-10-24<BR>


<P>[Moved to DR at the October, 2012 meeting.]</P>



<P>Both paragraphs 3 and 4 (for non-aggregate and aggregate
types, respectively) of 12.2.4.2.6 [<A href="https://wg21.link/over.ics.list">over.ics.list</A>] say that
the implicit conversion sequence is a user-defined conversion
sequence, but neither specifies that the second standard
conversion sequence is the identity conversion, as is presumably
intended.  This makes ranking by 12.2.4.3 [<A href="https://wg21.link/over.ics.rank">over.ics.rank</A>]
bullet 3.2 unncessarily unclear.</P>

<P><B>Proposed resolution (February, 2012):</B></P>

<P>Change 12.2.4.2.6 [<A href="https://wg21.link/over.ics.list">over.ics.list</A>] paragraphs 3-4 as follows:</P>

<BLOCKQUOTE>

<P>Otherwise, if the parameter is a non-aggregate class <TT>X</TT> and
overload resolution per 12.2.2.8 [<A href="https://wg21.link/over.match.list">over.match.list</A>] chooses a single
best constructor of <TT>X</TT> to perform the initialization of an
object of type <TT>X</TT> from the argument initializer list, the
implicit conversion sequence is a user-defined conversion sequence
<INS>with the second standard conversion sequence an identity
conversion</INS>.  If multiple constructors are viable but none is
better than the others, the implicit conversion sequence is the
ambiguous conversion sequence...</P>

<P>Otherwise, if the parameter has an aggregate type which can be
initialized from the initializer list according to the rules for
aggregate initialization (9.5.2 [<A href="https://wg21.link/dcl.init.aggr">dcl.init.aggr</A>]), the implicit
conversion sequence is a user-defined conversion sequence <INS>with
the second standard conversion sequence an identity
conversion</INS>. [<I>Example:</I>...</P>

</BLOCKQUOTE>

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