Re: ada paper critic

[Jeffrey Carter <jrcarter@acm.org>]

Robert A Duff wrote:
> 
> Jeffrey Carter <jrcarter@acm.org> writes:
> 
> > This seems to be an incomplete sentence. If I interpret it correctly,
> > the Ada intent is that the information be carried primarily by the
> > exception name. You should not be using a single exception and
> > differentiating between logical exceptions by the information attached
> > to that exception.
> 
> The problem with this view is that it forces the designer of an
> abstraction to decide on the granularity of exception handling, when
> this decision rightly belongs in the hands of the person designing the
> *handler*.  In fact, different handlers have different requirements:
> e.g., one handler might want to handle all I/O errors, whereas another
> one might want to handle disk_full_error specially.  If the designer of
> the abstraction decided to lump all I/O errors under one exception name,
> then the fine-grained handler is impossible to write.  On the other
> hand, if the designer of the abstraction defined many exceptions for
> different kinds of I/O errors, then the coarse-grained handler has to
> mention them all, which is overly verbose, and unmaintainable, because
> there might be a new kind of I/O error invented tomorrow.

I disagree. The designer of the abstraction has no choice; he must use
fine-grained exceptions so that a client with fine-grained handling
needs is not excluded. This is true regardless of whether the language
has hierarchical exceptions.

However, this is irrelevant to the original post to which I was
replying. It claimed that the use of String to attach information to an
exception made exceptions in Ada inherently slow.

> > Also, exceptions should only be used for exceptional situations, so this
> > does not impact normal processing at all.
> 
> I don't see how that's relevant.  A bug in exception handling is a bug,
> even though exceptions occur only rarely.

Again, this was in the context of exceptions impacting execution speed,
not of errors.

-- 
Jeff Carter
"You cheesy lot of second-hand electric donkey-bottom biters."
Monty Python & the Holy Grail