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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

  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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