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    CWG Issue 1911</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="1911"></A><H4>1911.
  
<TT>constexpr</TT> constructor with non-literal base class
</H4>
<B>Section: </B>9.2.6&#160; [<A href="https://wg21.link/dcl.constexpr">dcl.constexpr</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

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

 <B>Date: </B>2014-04-13<BR>


<P>[Moved to DR at the November, 2014 meeting.]</P>



<P>An example like</P>

<PRE>
  struct X {
    std::unique_ptr&lt;int&gt; p;
    constexpr X() { }
  };
</PRE>

<P>is ill-formed because the <TT>X</TT> constructor cannot be used
in a constant expression, because a constant expression cannot
construct an object of a non-literal type like <TT>unique_ptr</TT>.
This prevents use of something like</P>

<PRE>
  X x;
</PRE>

<P>to guarantee constant-initialization.</P>

<P><B>Proposed resolution (June, 2014):</B></P>

<P>Change 9.2.6 [<A href="https://wg21.link/dcl.constexpr#5">dcl.constexpr</A>] paragraph 5 as follows:</P>

<BLOCKQUOTE>

For a non-template, non-defaulted <TT>constexpr</TT> function or a
non-template, non-defaulted, non-inheriting <TT>constexpr</TT> constructor,
if no argument values exist such that an invocation of the function or
constructor could be an evaluated subexpression of a core constant
expression (7.7 [<A href="https://wg21.link/expr.const">expr.const</A>]), <INS>or, for a constructor,
a constant initializer for some object (6.10.3.2 [<A href="https://wg21.link/basic.start.static">basic.start.static</A>]),</INS>
the program is ill-formed; no diagnostic required.

</BLOCKQUOTE>

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