Re: Structured exception information

[Ray Blaak <rAYblaaK@STRIPCAPStelus.net>]

Stephen Leake <stephen_leake@stephe-leake.org> writes:
> Maciej Sobczak <no.spam@no.spam.com> writes:
> > Doesn't feel as type-safe as advertised.
> 
> But you have not given an actual example where a string is not
> a type-safe solution to the actual problem at hand.
> 
> The only example you have given is "present the error to the user". In
> that case, a string is precisely the correct type.

A common example I run into is to have the exception contain user-level versus
detailed information. The top exception handler will tend to present the
user-level information as a popup dialog, whereas the detailed information
will be logged for later analysis, sent out as a bug report, etc.

Often the detailed information could have various numeric values, e.g. source
locations for parse errors.

Even if both the user and detailed information are simple strings, one still
has two strings, and it is a pain to have to come up with an encoding scheme
(e.g. xml) and parse them back out when handled.

Usage should be able to be simple and direct.

> If you look into the details of "structured exception handling" in
> other languages and implementations, they have bugs, and fundamental
> flaws in design. [...]
> So if you find yourself fighting Ada to do something, you need to step
> back and think more carefully about _why_ you are doing it that way.
> Ada is telling you it is inherently unsafe.

The usage I described above is perfectly safe and bug free in all other
languages I use, even C++. 

It is also convenient.

Ada's philosophy is "correct", but the convenience can certainly be improved
in this area.

Consider also that any serialization scheme into exception strings is itself
more complex and thus more likely to be buggy.

-- 
Cheers,                                        The Rhythm is around me,
                                               The Rhythm has control.
Ray Blaak                                      The Rhythm is inside me,
rAYblaaK@STRIPCAPStelus.net                    The Rhythm has my soul.