🚀 go-pugleaf

In article <494oog$hmf@gabi.gabi-soft.fr>,
   kanze@gabi-soft.fr (J. Kanze) wrote:
>Fergus Henderson (fjh@munta.cs.mu.OZ.AU) wrote:
>|> schuenem@informatik.tu-muenchen.de (Ulf Schuenemann) writes:
>|> >How about saying that dtors have an empty exception-specification 
>|> >(either by default or always) ?
>
>|> How does that help?

I think he wants unexpected() to be called, rather than an inelegant 
terminate(), when a dtor throws during unwinding.

>|> >Then there are 3 cases possible:
>|> >- The dtor causes no eception.
>|> >- The dtor catches all exceptions and continues - save,
>|> >  but what happens to client-provided exception handling ?
>|> >- The dtor does not handle an exception that happend to be
>|> >  be raised - unexpected() is called.
>
>|> Yes, and what if the programmer has defined unexpected()
>|> to rethrow the exception?  (In most circumstances, doing so
>|> is probably a much better idea than just crashing via
>|> a call to abort().)
>
>1. How can it know what the exception was to rethrow it?  Is a throw
>without an argument legal here?  (I don't think so, but I'm not sure.)
	
I was about to say that it must be legal -- this is precisely what Cline and 
Lomow suggest in their FAQ book (FAQ #271).  However:

>2. This behavior doesn't seem conform to the required behavior in
>18.6.1.2.  I believe that when a user provided routine violates required
>behavior, undefined behavior results.

[Note: 18.6.1.2 in the April draft is now 18.6.2.2 in the Sept WP.]

It seems you're right, since the unexpected_handler isn't supposed to throw 
the same (unexpected) exception again.  Relevant section follows (from the 
Sept WP; the April draft looks identical):

---8<---8<----------------------------------------------------------------
  Required behavior:
    an  unexpected_handler  shall either throw an exception or terminate
    execution of the program without returning to the caller.  An  unex­
    pected_handler may perform any of the following:

  --throw an exception that satisfies the exception specification;
  --throw a bad_exception exception;
  --call terminate();
  --call either abort() or exit();

  Default behavior:
    The implementation's default unexpected_handler calls terminate().
---8<---8<----------------------------------------------------------------

Is disallowing a rethrow deliberate, or something that could be relaxed to 
allow rethrowing as Cline and Lomow suggest?

Herb


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