<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1129</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<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="1129"></A><H4>1129.
  
Default <TT>nothrow</TT> for <TT>constexpr</TT> functions
</H4>
<B>Section: </B>9.2.6&#160; [<A href="https://wg21.link/dcl.constexpr">dcl.constexpr</A>]
 &#160;&#160;&#160;

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

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

 <B>Date: </B>2010-08-02<BR><BR>


<P>[Voted into the WP at the November, 2010 meeting.]</P>

<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3296.html#GB29">N3092 comment
  GB&#160;29<BR></A>

<P>A <TT>constexpr</TT> function is not permitted to return via an
exception. This should be recognised, and a function
declared <TT>constexpr</TT> without an explicit exception
specification should be treated as if declared
<TT>noexcept(true)</TT> rather than the usual
<TT>noexcept(false)</TT>. For a function template declared
<TT>constexpr</TT> without an explicit exception specification, it
should be considered <TT>noexcept(true)</TT> if and only if the
<TT>constexpr</TT> keyword is respected on a given
instantiation. </P>

<P>See also <A HREF="1125.html">issue 1125</A>.</P>

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

<P>The premise is not correct: an exception is forbidden only when a
<TT>constexpr</TT> function is invoked in a context that requires
a constant expression. Used as an ordinary function, it can throw.</P>

<P><B>Proposed resolution (August, 2010):</B></P>

<P>Change 7.6.2.7 [<A href="https://wg21.link/expr.unary.noexcept#3.1">expr.unary.noexcept</A>] bullet 3.1 as follows:</P>

<UL><LI>a potentially evaluated call<SUP>80</SUP> to a
function, member function, function pointer, or member
function pointer that does not have a non-throwing
<I>exception-specification</I> (14.5 [<A href="https://wg21.link/except.spec">except.spec</A>]),
<INS>unless the call is a constant expression (7.7 [<A href="https://wg21.link/expr.const">expr.const</A>]),</INS>
</LI></UL>

<BR><BR>
</BODY>
</HTML>
