Re: Common exception handling

[Martin <martin.dowie@btopenworld.com>]

On Aug 29, 4:31 pm, Adam Beneschan <a...@irvine.com> wrote:
> On Aug 29, 1:32 am, Martin <martin.do...@btopenworld.com> wrote:
>
>
>
> > On 26 Aug, 15:43, Adam Beneschan <a...@irvine.com> wrote:
>
> > > On Aug 26, 6:47 am, shaunpatter...@gmail.com wrote:
>
> > > > Yeah, it looks like the extra layer of exception handling is the only
> > > > way. I was hoping I could avoid that if possible.
>
> > > No, I don't think it's the only way.  I'm surprised no one has
> > > suggested this:
>
> > >    exception
> > >       when E : others =>
> > >          Print_Test (Rec);
> > >          declare
> > >              use Ada.Exceptions;
> > >          begin
> > >              if Exception_Identity(E) = A'Identity then
> > >                 ... handling for A
> > >              elsif Exception_Identity(E) = B'Identity then
> > >                 ... handling for B
> > >              etc.
> > >              else
> > >                 ... handling for other exceptions you didn't expect,
> > >                 ... but you certainly need to aware that it could
> > >                 ... happen
> > >                 raise;  --maybe
> > >              end if;
> > >          end;
>
> > >                             -- Adam
>
> > Surely you missed a smiley off this suggestion!!! :-)
>
> Well, I do often post silly things without smileys and assume everyone
> is astute enough to figure out that I was trying to be funny.  But I
> wasn't being funny here.  Although the above looks somewhat ugly, I
> can imagine that a solution of this sort may be entirely appropriate
> in some cases. Suppose, for example, that the common code isn't just
> at the beginning, but is also at the end, or maybe even in the middle;
> the nested exception handler/reraise solution might not be so clean in
> that case.  Another problem with the nested exception handler solution
> is that it could incur extra overhead since exception raising isn't
> necessarily cheap.  That shouldn't matter in most cases, but sometimes
> it might.  So I don't understand why the above is so ridiculous as to
> merit the comment you gave.
>
> I would say, though, that if your exception-handling code gets that
> complex, it might be time to think about declaring just one exception
> and a separate data structure for passing additional exception info
> around.
>
>                                  -- Adam

Sorry - back again!

It was mostly the (to my eyes) sheer "ugliness" of the
if..elsif..elsif..end if;.

I find these sorts of structures very hard to follow (was there a
sneeky 'and then <boolean_expression>' snuck into one of the
branches???

-- Martin