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    CWG Issue 1381</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="1381"></A><H4>1381.
  
Implicitly-declared special member functions and default <TT>nothrow</TT>
</H4>
<B>Section: </B>14.5&#160; [<A href="https://wg21.link/except.spec">except.spec</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD3
 &#160;&#160;&#160;

 <B>Submitter: </B>David Svoboda
 &#160;&#160;&#160;

 <B>Date: </B>2011-08-26<BR>


<P>[Moved to DR at the October, 2012 meeting.]</P>

<P>According to 14.5 [<A href="https://wg21.link/except.spec#14">except.spec</A>] paragraph 14,</P>

<BLOCKQUOTE>

An implicitly declared special member function (11.4.4 [<A href="https://wg21.link/special">special</A>]) shall
have an <I>exception-specification</I>.  If <TT>f</TT> is an implicitly declared
default constructor, copy constructor, move constructor,
destructor, copy assignment operator, or move assignment
operator, its implicit <I>exception-specification</I> specifies the
<I>type-id</I> <TT>T</TT> if and only if <TT>T</TT> is allowed by the
<I>exception-specification</I> of a function directly invoked by
<TT>f</TT>'s implicit definition; <TT>f</TT> shall allow all
exceptions if any function it directly invokes allows all
exceptions, and <TT>f</TT> shall allow no exceptions if every
function it directly invokes allows no exceptions.

</BLOCKQUOTE>

<P>It would be clearer if this description made explicit the intent
that special member functions that invoke no other functions are to
allow no exceptions.</P>

<P><B>Proposed resolution (February, 2012):</B></P>

<P>Change 14.5 [<A href="https://wg21.link/except.spec#14">except.spec</A>] paragraph 14 as follows:</P>

<BLOCKQUOTE>

<P>...and <TT>f</TT> has the <I>exception-specification</I>
<TT>noexcept(true)</TT> if every function it directly invokes allows
no exceptions. <INS>[<I>Note:</I> It follows that <TT>f</TT> has the
<I>exception-specification</I> <TT>noexcept(true)</TT> if it invokes
no other functions. &#8212;<I>end note</I>]</INS> [<I>Example:</I>
</P>

<PRE>
  struct A {
    A();
    A(const A&amp;) throw();
    A(A&amp;&amp;) throw();
    ~A() throw(X);
  };
  struct B {
    B() throw();
    B(const B&amp;) <DEL>throw()</DEL> <INS>= default</INS>;  <INS>//<SPAN CLASS="cmnt"> Declaration of </SPAN>B::B(const B&amp;) noexcept(true)</INS>
    B(B&amp;&amp;) throw(Y);
    ~B() throw(Y);
  };
  ...
</PRE>

</BLOCKQUOTE>

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