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    CWG Issue 1099</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="1099"></A><H4>1099.
  
Infinite recursion in <TT>constexpr</TT> functions
</H4>
<B>Section: </B>7.7&#160; [<A href="https://wg21.link/expr.const">expr.const</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>Jason Merrill
 &#160;&#160;&#160;

 <B>Date: </B>2010-08-01<BR>


<P>[Voted into the WP at the March, 2011 meeting.]</P>



<P>It is not clear what happens when a program violates the limits on
constexpr function recursion in a context that does not require a
constant expression.  For example,</P>

<PRE>
  constexpr int f(int i) { return f(i); }
  const int i = f(1);   //<SPAN CLASS="cmnt"> error, undefined behavior, or dynamic initialization?</SPAN>
</PRE>

<P>(Presumably the &#8220;within its resource limits&#8221; caveat of
4.1 [<A href="https://wg21.link/intro.compliance#2">intro.compliance</A>] paragraph 2 would effectively result in
undefined behavior in a context that required a constant expression.)</P>

<P><B>Notes from the November, 2010 meeting:</B></P>

<P>The CWG was of mixed opinion as to whether an infinite recursion
in a constexpr function should be ill-formed or simply render an
expression non-constant.</P>

<P><B>Proposed resolution (January, 2011):</B></P>

<P>Add the following bullet in 7.7 [<A href="https://wg21.link/expr.const#2">expr.const</A>] paragraph 2:</P>

<UL><LI><P><INS>an invocation of a <TT>constexpr</TT> function or a
<TT>constexpr</TT> constructor that would exceed the
implementation-defined recursion limit (see annex Clause Annex B [<A href="https://wg21.link/implimits">implimits</A>]);</INS></P></LI></UL>

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