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    CWG Issue 2336</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="2336"></A><H4>2336.
  
Destructor characteristics vs potentially-constructed subobjects
</H4>
<B>Section: </B>14.5&#160; [<A href="https://wg21.link/except.spec">except.spec</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD5
 &#160;&#160;&#160;

 <B>Submitter: </B>Nathan Sidwell
 &#160;&#160;&#160;

 <B>Date: </B>2017-02-28<BR>


<P>[Accepted as a DR at the February, 2019 meeting.]</P>

<P>According to 14.5 [<A href="https://wg21.link/except.spec#8">except.spec</A>] paragraph 8,</P>

<BLOCKQUOTE>

The exception specification for an implicitly-declared
destructor, or a destructor without a <I>noexcept-specifier</I>,
is potentially-throwing if and only if any of the destructors for
any of its potentially constructed subojects is potentially
throwing.

</BLOCKQUOTE>

<P>11.4.4 [<A href="https://wg21.link/special#5">special</A>] paragraph 5 defines &#8220;potentially
constructed subobjects&#8221; as follows:</P>

<BLOCKQUOTE>

For a class, its non-static data members, its non-virtual direct
base classes, and, if the class is not abstract
(11.7.4 [<A href="https://wg21.link/class.abstract">class.abstract</A>]), its virtual base classes are called
its potentially constructed subobjects.

</BLOCKQUOTE>

<P>This leads to the following problem:</P>

<PRE>
  class V {
  public:
    virtual ~V() noexcept(false);
  };

  class B : virtual V {
    virtual void foo () = 0;
    //<SPAN CLASS="cmnt"> implicitly defined </SPAN>virtual ~B () noexcept(true);
  };

  class D : B {
    virtual void foo ();
    //<SPAN CLASS="cmnt"> implicitly defined </SPAN>virtual ~D () noexcept(false);
  };
</PRE>

<P>Here, <TT>D::~D()</TT> is throwing but overrides the non-throwing
<TT>B::~B()</TT>.</P>

<P>There are similar problems with the deletedness of
destructors per 11.4.7 [<A href="https://wg21.link/class.dtor#5">class.dtor</A>] paragraph 5, which
also only considers potentially constructed subobjects.</P>

<P><B>Proposed resolution (November, 2018):</B></P>

<P>Change 14.5 [<A href="https://wg21.link/except.spec#8">except.spec</A>] paragraph 8 as follows:</P>

<BLOCKQUOTE>

The exception specification for an implicitly-declared
destructor, or a destructor without
a <I>noexcept-specifier</I>, is potentially-throwing if and
only if any of the destructors for any of its potentially
constructed subobjects is <DEL>potentially throwing</DEL>
<INS>potentially-throwing or the destructor is virtual and
the destructor of any virtual base class is
potentially-throwing</INS>.

</BLOCKQUOTE>

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