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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Thu, 10 Mar 2005 11:13:20 +0100
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Date: 2005-03-10T11:13:20+01:00
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Randy Brukardt wrote:
> "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. 

Ahhh. Here is the trick :)

I must re-read the gnat advance on 2005 features. There are a lot of 
exciting changes coming.

> 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