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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re:
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Date: Sat, 26 Mar 2011 08:02:45 +0100
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Date: 2011-03-26T08:02:44+01:00
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On Fri, 25 Mar 2011 16:45:28 +0100, Yannick Duchêne (Hibou57) wrote:

> I remember some peoples says here, this is a pity to have “not null”  
> annotations, while the case which should be clearly marked, is the one  
> where a reference may be null. I'm OK with that principle. But concretely  
> what would have been the notation ? “may be null” ? Two reserved words  
> added for that ? A simple “null” would not have been really expressive  
> (just a though I get right a few minutes ago).

No notation needed. Before Ada 2005 broke it, "access T" was not null, if
anonymous type is what you mean.

Named type is a different beast. When you declare a named access type "not
null" is a constraint. You cannot have a constrained subtype before the
type.

Yet another story is an access type, which does not have null as a value.
It is not much different from being constrained. Compare it with integer
types. When you declare:

   type P is range 1..2;

You do not eliminate 0, as you might think. P has a "parent type," which
still has 0 (P'Base).

So which case you meant? (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de