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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Wed, 9 Mar 2005 16:43:11 -0600
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Date: 2005-03-09T16:43:11-06:00
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"Alex R. Mosteo" <devnull@mailinator.com> wrote in message
news:422F142E.9050909@mailinator.com...
> This is something I don't fully understand. IFAIK,
>
> procedure Proc (Blah : access Some_Type);
>
> access parameters raise an excepcion if null.

Not in Ada 2005. That restriction makes it very difficult to do C
interfacing, among other things. Moreover, keeping the restriction would
have made the expansion of anonymous access types to most contexts unusable
(you need a null value sometimes!). The only case where "not null" is
implicit is if the parameter is controlling (that's necessary for
compatibility - I think most of us hate it, but there doesn't seem to be an
alternative).

> So I don't get what adds
> to the language the
>
> Blah : not null access ...
>
> construct.

Because it (a) makes the restriction explicit, and (b) you can use it
anywhere: on named access types, on variables and components, in generic
formals, etc.

   type Acc is access Some_Type;
   procedure Proc (P : in not null Acc);

                               Randy Brukardt