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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: Handling invalid objects
Date: Mon, 20 Mar 2006 17:44:06 -0600
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Date: 2006-03-20T17:44:06-06:00
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"Justin Gombos" <rpbkbq.xax.gld@uluv.kbq> wrote in message
news:41LSf.4126$TK2.1805@trnddc07...
> On 2006-03-18, Randy Brukardt <randy@rrsoftware.com> wrote:
> >
> > You're confusing an "invalid" object with an "abnormal"
> > object. Accessing an abnormal one is erroneous; surely you don't
> > want to intentionally put that into your programs. (Remember,
> > "erroneous" is Ada-speak for "anything at all can happen".)
>
> The 'Valid attribute exists to be able to handle abnormal objects.

No, it exists to handle *invalid* objects. It has no effect on *abnormal*
objects. Please be careful with your terminology here because using the
*abnormal* the way you are is very confusing. I'm using the terminology
defined in the Standard: see
http://www.adaic.com/standards/05aarm/html/AA-13-9-1.html (or the similar
section in the Ada 95 manual) to see the definitions of the terms.

> Here's a concrete example.  Suppose I have:

Your example shows *invalid* values, not *abnormal* values.

...
> Exceptions are a poor choice.

No, I think they're the right choice here (presuming you are talking about
clock failure or some other unusual event).

> The quality and style guide advises against them for a good
> reason; exceptions are like gotos - and produce a questionable state.

The state isn't questionable in this case: you have no legitimate value to
return, so anything you return is garbage. That means there isn't any state
to corrupt.

                        Randy.