From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Issue with GNAT GPL 2009 and GtkAda
Date: Fri, 26 Jun 2009 10:52:27 +0200
Date: 2009-06-26T10:52:27+02:00 [thread overview]
Message-ID: <1hi0km5xe1802.17l3qjn1g9525$.dlg@40tude.net> (raw)
In-Reply-To: 4a44842e$0$31872$9b4e6d93@newsspool3.arcor-online.net
On Fri, 26 Jun 2009 10:17:49 +0200, Georg Bauhaus wrote:
> Dmitry A. Kazakov wrote:
>
>> Access types are much overused in Ada in order to overcome language
>> problems unrelated to access types.
>
> Another reason to overuse _anonymous_ access types is
> probably outside the language, but is present with language
> users: anonymity provides for a reduction in perceived
> programmer typing cost which is a convincing motive
> to not use names in practice. I.e.
>
> type R is record
> C1 : access T; -- quick & risky
> C2 : Float;
> end record
>
> is thought to bring less work.
One of the language problems is that the container types do not well
compose unconstrained types. Considering this one:
type R is record
C1 : T'Class; -- does not work, considering an access type
C2 : Float;
end record
it should be allowed to do without access types, like:
type R (Constraint : T'Range) is record
C1 : T'Class (Constraint); -- Still class-wide, but constrained
C2 : Float;
end record
T'Range is a subtype of Ada.Tags.Tag:
subtype T'Range is T'Tag...<the last tag of types derived from T>;
> Experience apparently shows that
> it doesn't, since the anonymity virus becomes activated sooner
> or later. (Judging by the number of reports of anonymous access
> issues.)
Yes. I think it is related to a more general issue of structural vs.
nominal type equivalence. I suspect that structural equivalence never pays
off. Ada, initially designed with nominal equivalence, swayed to the
structural one. Anonymous access types is the most prominent example of.
> Does "access T :=" really have 80/20 merits?
I would remove anonymous access types altogether, fixing the real language
problems, which led to introducing them in first place.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2009-06-26 8:52 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-23 21:52 Issue with GNAT GPL 2009 and GtkAda Damien Carbonne
2009-06-24 7:40 ` Dmitry A. Kazakov
2009-06-24 10:15 ` Stephen Leake
2009-06-25 9:06 ` Stephen Leake
2009-06-25 9:39 ` Dmitry A. Kazakov
2009-06-25 19:02 ` Damien Carbonne
2009-06-26 9:31 ` Stephen Leake
2009-06-26 11:18 ` Niklas Holsti
2009-06-26 16:29 ` Damien Carbonne
2009-06-26 17:28 ` Dmitry A. Kazakov
2009-06-26 19:27 ` Damien Carbonne
2009-06-26 19:50 ` Dmitry A. Kazakov
2009-06-26 21:51 ` Randy Brukardt
2009-06-27 11:11 ` Stephen Leake
2009-06-27 17:04 ` Robert A Duff
2009-06-30 11:11 ` Stephen Leake
2009-06-30 18:10 ` Robert A Duff
2009-06-29 22:11 ` Randy Brukardt
2009-06-30 11:13 ` Stephen Leake
2009-06-30 15:26 ` Adam Beneschan
2009-06-30 15:59 ` Adam Beneschan
2009-06-30 23:11 ` Randy Brukardt
2009-06-27 9:56 ` Stephen Leake
2009-06-26 21:03 ` Damien Carbonne
2009-06-27 11:21 ` Stephen Leake
2009-06-27 12:25 ` Damien Carbonne
2009-06-27 12:35 ` Damien Carbonne
2009-06-29 22:15 ` Randy Brukardt
2009-07-01 19:22 ` Damien Carbonne
2009-06-30 0:48 ` Adam Beneschan
2009-06-30 11:18 ` Stephen Leake
2009-06-25 20:49 ` Randy Brukardt
2009-06-26 7:20 ` Dmitry A. Kazakov
2009-06-26 8:17 ` Georg Bauhaus
2009-06-26 8:52 ` Dmitry A. Kazakov [this message]
2009-06-26 21:38 ` Randy Brukardt
2009-06-27 7:47 ` Dmitry A. Kazakov
2009-06-29 21:59 ` Randy Brukardt
2009-06-30 8:31 ` Dmitry A. Kazakov
2009-06-26 21:31 ` Randy Brukardt
2009-06-27 7:53 ` Dmitry A. Kazakov
2009-06-26 8:39 ` Alex R. Mosteo
2009-06-26 9:07 ` Dmitry A. Kazakov
2009-06-27 9:53 ` Stephen Leake
2009-06-26 21:40 ` Randy Brukardt
2009-06-29 10:04 ` Alex R. Mosteo
2009-06-26 9:02 ` Stephen Leake
2009-06-26 9:14 ` Dmitry A. Kazakov
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