From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: GNAT GPL 2013 bug?
Date: Mon, 12 Aug 2013 19:03:14 +0200
Date: 2013-08-12T19:03:14+02:00 [thread overview]
Message-ID: <1evw1coxfrfu5$.1atfpln47qs0j.dlg@40tude.net> (raw)
In-Reply-To: 4589f4c3-a1c7-4fa7-9b79-89a9917502bf@googlegroups.com
On Mon, 12 Aug 2013 09:52:29 -0700 (PDT), Adam Beneschan wrote:
> On Friday, August 9, 2013 11:51:34 PM UTC-7, Dmitry A. Kazakov wrote:
>> On Fri, 09 Aug 2013 16:04:02 -0400, Robert A Duff wrote:
>
>> I can "dispatch" on null anyway:
>>
>> type T is tagged null record;
>> procedure P (X : T) is null;
>> procedure R (X : access T'Class);
>>
>> procedure R (X : access T'Class) is
>> begin
>> X.P;
>> end R;
>
> But I could write
>
> procedure R (X : access T'Class) is
> begin
> if X = null then
> -- take some special default action
> else
> X.P;
> end if;
> end R;
>
> The point is that when a caller calls R, the above procedure is simply
> called. So it will work to call it with a null parameter; the code in R
> may later run into a Constraint_Error or not, depending on how it's
> written, but there's no problem calling R. But when P is called, the
> dispatching occurs *at* *that* *point*, before any code in any of the P
> procedures is executed;
It is irrelevant for the client (= user = program semantics) where that
check is placed, an implementation detail, nothing more.
> if the parameter is null, the dispatch cannot
> work.
>
> I'm really not clear at all on what point you're trying to make.
That implied null-exclusion for controlling parameters does not change/save
anything. Just added language weirdness that
"access T" is subtype conformant to "not null access T" depending on T
!, for apparently no gain.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2013-08-12 17:03 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-09 9:47 GNAT GPL 2013 bug? Dmitry A. Kazakov
2013-08-09 10:38 ` sbelmont700
2013-08-09 11:01 ` Dmitry A. Kazakov
2013-08-09 11:06 ` sbelmont700
2013-08-09 11:36 ` Dmitry A. Kazakov
2013-08-09 15:48 ` Adam Beneschan
2013-08-09 16:11 ` Simon Wright
2013-08-09 16:52 ` Adam Beneschan
2013-08-09 18:25 ` Simon Wright
2013-08-09 18:39 ` Adam Beneschan
2013-08-09 19:28 ` Adam Beneschan
2013-08-09 20:05 ` Robert A Duff
2013-08-09 20:30 ` Adam Beneschan
2013-08-09 21:35 ` Simon Wright
2013-08-10 15:10 ` Shark8
2013-08-09 16:03 ` Simon Wright
2013-08-09 18:55 ` Randy Brukardt
2013-08-09 19:27 ` Dmitry A. Kazakov
2013-08-09 20:04 ` Robert A Duff
2013-08-10 6:51 ` Dmitry A. Kazakov
2013-08-12 16:52 ` Adam Beneschan
2013-08-12 17:03 ` Dmitry A. Kazakov [this message]
2013-08-12 17:20 ` Adam Beneschan
2013-08-12 18:34 ` Dmitry A. Kazakov
2013-08-12 20:12 ` Randy Brukardt
2013-08-13 6:43 ` Dmitry A. Kazakov
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