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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: Type safety on wikipedia
Date: Mon, 30 Jan 2006 20:13:52 -0600
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Date: 2006-01-30T20:13:52-06:00
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"Jan Andres" <jandres@gmx.net> wrote in message
news:dreihb$712$1@pitr.home.jan...
...
> Hmm, but aren't all the restrictions on the scope of access values
> actually there in order to guarantee type safety, as long as no unsafe
> constructs like 'Unchecked_Access are used? Or is
> Unchecked_Deallocation itself considered to be such an unsafe construct?
> If so, is there any "safe" alternative in Ada that we can use if we
> don't have GC?
>
> Of course you could simply avoid such constructs as quoted above but
> the downside is that the language will not actually enforce this.

The language (well, a compiler) can be made to enforce "No
Unchecked_Deallocation" using pragma Restrictions
(No_Unchecked_Deallocation); Similarly, you can prevent the use of
'Unchecked_Access with pragma Restrictions (No_Unchecked_Access); [Note that
these are program-wide, which might restrict the standard packages that you
can use.]

You can avoid using Unchecked_Deallocation if you can arrange for the access
type itself to go away, and then use a storage_pool for the storage. Or,
sometimes, you never need to free the data structure anyway (a compiler
symbol table comes to mind; it exists until the compile finishes). But both
of those are often impractical.

                                 Randy.