Re: Help Me Please :)

[Robert A Duff <bobduff@world.std.com>]

Richard D Riehle <laoXhai@ix.netcom.com> writes:

> In some languages, exceptions are first class objects.  Ada exceptions are
> not first class objects for very good reasons.
                              ^^^^^^^^^^^^^^^^^

I beg to differ.  I think this is one of the few cases where those other
languages got it right, and Ada got it wrong.

If you want strings, Ada.Exceptions works OK (although it's annoying to
have "exceptions" and "Exception_Ids", which are both essentially
representations of the same concept).  If you want to attach some other
type of data to an exception, you're stuck with several poor
alternatives: You could encode that data as a String, but then you lose
type checking -- the declaration of an exception ought to declare the
type of attached data, forming a compile-time-checkable contract between
the raise point and the handler point.  Or you could store the
information in a global, but then you lose task safety, and there are
issues of exactly when that global data is valid.  Etc.

- Bob