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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: Wed, 20 Jul 2005 22:23:45 -0500
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Date: 2005-07-20T22:23:45-05:00
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"Simon Wright" <simon@pushface.org> wrote in message
news:m2k6jmaw9n.fsf@grendel.local...
> Matthew Heaney <matthewjheaney@earthlink.net> writes:
>
> > Access types wouldn't work, since you would have to declare the
> > container element as "aliased" in order to return an access value,
> > but that would constrain the object (fix the value of the
> > discriminant).
>
> Is this still true in 0Y?

No. Virtually all of those rules were repealed; they made no sense and
didn't really fix the real problem. The better solution was to make some
access subtypes illegal instead. (If you don't even know what an access
subtype is, you're not alone. I don't think I've ever used one in 20+ years
of Ada programming.)

So we could have used access types rather than defining cursors, but we
didn't do it because access types can never be safe in this case, while
cursors can be checked. Similarly, we use a call-back procedure in
Update_Element rather than an access type, because we can check for abuse in
the routine.

                     Randy.