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    CWG Issue 2252</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="2252"></A><H4>2252.
  
Enumeration list-initialization from the same type
</H4>
<B>Section: </B>9.5.5&#160; [<A href="https://wg21.link/dcl.init.list">dcl.init.list</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

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

 <B>Date: </B>2016-03-22<BR>


<P>[Accepted as a DR at the November, 2023 meeting.]</P>



<P>According to 9.5.5 [<A href="https://wg21.link/dcl.init.list#3.8">dcl.init.list</A>] bullet 3.8,</P>

<BLOCKQUOTE>

Otherwise, if <TT>T</TT> is an enumeration with a fixed underlying type
(9.8.1 [<A href="https://wg21.link/dcl.enum">dcl.enum</A>]), the <I>initializer-list</I> has a single
element <TT>v</TT>, and the initialization is direct-list-initialization,
the object is initialized with the value <TT>T(v)</TT>
(7.6.1.4 [<A href="https://wg21.link/expr.type.conv">expr.type.conv</A>]); if a narrowing conversion is required to
convert <TT>v</TT> to the underlying type of <TT>T</TT> , the program is
ill-formed.

</BLOCKQUOTE>

<P>This could be read as requiring that there be a conversion from
<TT>v</TT> to the underlying type of <TT>T</TT>, leaving the status of an
example like the following unclear:</P>

<PRE>
  enum class E {};
  struct X { operator E(); };
  E{X()}; //<SPAN CLASS="cmnt"> ok? </SPAN>
</PRE>

<P><B>Notes from the March, 2018 meeting:</B></P>

<P>CWG disagreed that the existing wording requires such a conversion, only
that if such a conversion is possble, it must not narrow. A formulation
along the lines of &#8220;if that initialization involves a narrowing
conversion to the underlying type of <TT>T</TT>...&#8221; was suggested to
clarify the intent. This will be handled editorially, and the issue will be
left in "review" status until the change has been verified.</P>

<P><B>Additional notes (August, 2023)</B></P>

<P>
<A HREF="2374.html">Issue 2374</A> has meanwhile clarified
that <TT>v</TT> is required to implicitly convert to the underlying
type of the enumeration for 9.5.5 [<A href="https://wg21.link/dcl.init.list#3.8">dcl.init.list</A>] bullet 3.8 to
apply.  Now, the logic falls through to 9.5.5 [<A href="https://wg21.link/dcl.init.list#3.9">dcl.init.list</A>] bullet 3.9 for the above example, making it well-formed.</P>

<P><B>CWG 2023-09-15</B></P>

<P>Class types with conversions to scalar types were not in view when
the wording in this bullet was conceived.</P>

<P><B>Proposed resolution (approved by CWG 2023-10-06):</B></P>

<P>Change in 9.5.5 [<A href="https://wg21.link/dcl.init.list#3.8">dcl.init.list</A>] bullet 3.8 as follows:</P>

<BLOCKQUOTE>

Otherwise, if T is an enumeration with a fixed underlying type
(9.8.1 [<A href="https://wg21.link/dcl.enum">dcl.enum</A>]) U, the initializer-list has a single
element v <INS>of scalar type</INS>, v can be implicitly converted to
U, and the initialization is direct-list-initialization, the object is
initialized with the value T(v) (7.6.1.4 [<A href="https://wg21.link/expr.type.conv">expr.type.conv</A>]); if a
narrowing conversion is required to convert v to U, the program is
ill-formed.

</BLOCKQUOTE>

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