Re: Common exception handling

[Adam Beneschan <adam@irvine.com>]

On Aug 26, 8:10 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Tue, 26 Aug 2008 07:43:20 -0700 (PDT), Adam Beneschan 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;
>
> Hmm, it looks quite ugly, IMO. Exception handler (case-like) is better
> structured, cleaner, and possibly more efficient.
>
> ---------
> If exceptions were first-class citizens allowed in case statements then:
>
>    exception
>       when E : others =>
>          Print_Test (Rec);
>          case E is            -- This is not Ada, alas!
>             when A => ...
>             when B => ...
>             when others => ...
>          end case;

Maybe this use of CASE should be allowed, even if we don't go all the
way and make exceptions first-class entities in other ways.  What does
anyone else think... would it be a worthwhile feature to propose
adding?  Or is it just too "special" (if we added this, others would
ask, well why shouldn't we allow CASE on a string, or a record, or a
container, or just expand it using some user-specified relational
operator so that we can use it for everything...)?

                            -- Adam