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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Legit Warnings or not
Date: Thu, 21 Jul 2011 16:39:32 +0200
Organization: cbb software GmbH
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Date: 2011-07-21T16:39:32+02:00
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On Thu, 21 Jul 2011 09:50:26 +0000 (UTC), Brian Drummond wrote:

> Interesting. Do you mean they allocate a new object?

New implementation of.

> Then how do they handle the following declarations   
>    X : aliased Warned_Person;
>    Y : access Warned_Person := X'access;
> when X.Name is resized?

There exist approaches to this:

1. The varying component can allocated outside the object. The object would
keep a reference to it.

2. The access types to the object can be fat pointers or indirect pointers.
E.g. Y may actually point to a descriptor keeping a pointer to the object.

3. "aliased" can be disabled for roaming objects.

4. Certain types of access can be disabled, eventually allowing only
downward closures of the object.

Except for #1 aliasing is a problem:

   procedure Foo (X : in out Warned_Person; Y : Warned_Person) is
   begin
      X := ...; -- Changes the object

   Foo (X, X); -- Will Y be consistent in Foo?

I think that Ada should not try to support this stuff. The proper way to
handle this IMO is to allow the programmer to implement it himself by
making the component "Name" a primitive operation (getter/setter). I don't
know how close "aspects" are to this but this would be the right way.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de