From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Proposal: Auto-allocation of Indefinite Objects
Date: Fri, 31 Jul 2020 12:20:07 +0200 [thread overview]
Message-ID: <rg0r8m$15rf$1@gioia.aioe.org> (raw)
In-Reply-To: cc57927c-715d-4259-8a87-1677bae3f5fen@googlegroups.com
On 31/07/2020 11:25, Stephen Davies wrote:
> On Friday, 3 April 2020 at 23:48:43 UTC+1, Stephen Davies wrote:
>> type Node_Type is record
>> Item : new Element_Type;
>> Prev : Node_Ptr_Type;
>> Next : Node_Ptr_Type;
>> end record;
>
> Perhaps a better way to think of this is as a discriminated record without
> an explicit discriminant? In which case maybe a different syntax than "new"
> would be appropriate?
That is right, but it would be a much larger problem to resolve than
your original proposal.
First, Ada lacks necessary discriminants, e.g.
type Node_Type (Descendant : Ada.Tags.Tag) is record
Item : Element_Type (Tag => Descendant);
Prev : Node_Ptr_Type;
Next : Node_Ptr_Type;
end record;
Here Element_Type is a specific type from Element_Type'Class which tag
is Descendant.
Second, Ada's object initialization process has no means to determine
discriminants. One extra step is missing before a call to allocator to
provide constraints of a type. [I proposed a record type T'Constraints
that would contain all constraints and no data to be passed to allocator
to determine the object constraints and thus its size.]
Third, there is still the problem that task components do not work, as
well as all other cases when the Rosen trick is used to work-around full
multiple inheritance by making record members out of intended parents.
All in one, the crude work-around has always been an access type, which
your original proposal would handle with much more grace.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2020-07-31 10:20 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-03 22:48 Proposal: Auto-allocation of Indefinite Objects Stephen Davies
2020-04-03 23:45 ` Stephen Leake
2020-04-04 10:54 ` Jeffrey R. Carter
2020-04-04 20:55 ` Stephen Davies
2020-04-04 8:31 ` Dmitry A. Kazakov
2020-07-27 7:47 ` Yannick Moy
2020-07-27 9:21 ` J-P. Rosen
2020-07-27 9:49 ` Dmitry A. Kazakov
2020-07-27 17:48 ` Brian Drummond
2020-07-27 20:02 ` Dmitry A. Kazakov
2020-07-28 14:28 ` Brian Drummond
2020-07-28 14:59 ` Dmitry A. Kazakov
2020-07-29 15:33 ` Brian Drummond
2020-07-29 16:20 ` Dmitry A. Kazakov
2020-07-30 13:37 ` Stephen Davies
2020-07-30 14:23 ` Dmitry A. Kazakov
2020-07-30 17:04 ` Brian Drummond
2020-07-30 18:28 ` Dmitry A. Kazakov
2020-08-10 0:39 ` Randy Brukardt
2020-08-10 8:57 ` Dmitry A. Kazakov
2020-08-20 0:10 ` Randy Brukardt
2020-08-20 17:49 ` Dmitry A. Kazakov
2020-08-20 20:19 ` Dennis Lee Bieber
2020-08-20 23:33 ` Randy Brukardt
2020-08-21 6:45 ` Dmitry A. Kazakov
2020-08-23 4:52 ` Randy Brukardt
2020-08-23 12:28 ` Dmitry A. Kazakov
2020-08-20 23:30 ` Randy Brukardt
2020-08-21 6:46 ` Dmitry A. Kazakov
2020-08-23 4:48 ` Randy Brukardt
2020-08-23 12:29 ` Dmitry A. Kazakov
2020-08-10 0:31 ` Randy Brukardt
2020-08-10 8:58 ` Dmitry A. Kazakov
2020-08-20 0:13 ` Randy Brukardt
2020-08-20 17:49 ` Dmitry A. Kazakov
2020-08-20 23:25 ` Randy Brukardt
2020-08-21 7:08 ` Dmitry A. Kazakov
2020-08-23 5:03 ` Randy Brukardt
2020-08-23 12:28 ` Dmitry A. Kazakov
2020-07-27 20:31 ` Jeffrey R. Carter
2020-07-31 9:25 ` Stephen Davies
2020-07-31 10:20 ` Dmitry A. Kazakov [this message]
2020-08-01 11:22 ` Stephen Davies
2020-08-01 12:58 ` Dmitry A. Kazakov
2020-08-01 20:35 ` Stephen Davies
2020-08-01 20:56 ` Dmitry A. Kazakov
2020-09-03 4:30 ` linda white
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