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    CWG Issue 831</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="831"></A><H4>831.
  
Limit on recursively nested template instantiations
</H4>
<B>Section: </B>Clause Annex B&#160; [<A href="https://wg21.link/implimits">implimits</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>DE
 &#160;&#160;&#160;

 <B>Date: </B>3 March, 2009<BR><BR>


<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3086.html#DE25">N2800 comment
  DE&#160;25<BR></A>

<P>[Voted into WP at October, 2009 meeting.]</P>

<P>The limit of 17 recursively-nested template instantiations is too
small for modern programming practices such as template metaprogramming.
It is unclear, however, whether this is a useful metric; see
<A href="http://ubiety.uwaterloo.ca/~tveldhui/papers/2003/turing.pdf">
this paper</A> for an example that honors the limit but results in
over 750 billion instantiations.</P>

<P><B>Notes from the July, 2009 meeting:</B></P>

<P>The consensus of the CWG was to increase the limit to 1024.</P>

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

<P>Change Clause Annex B [<A href="https://wg21.link/implimits">implimits</A>], the fourth bullet from the end, as follows:</P>

<UL><LI>Recursively nested template instantiations [<DEL>17</DEL>

<INS>1 024</INS>].</LI></UL>

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