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From: Shark8 <onewingedshark@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Preventing type extensions
Date: Fri, 17 Sep 2010 14:05:26 -0700 (PDT)
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Date: 2010-09-17T14:05:26-07:00
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On Sep 17, 1:04=A0am, AdaMagica <christoph.gr...@eurocopter.com> wrote:
> On 17 Sep., 02:16, Shark8 <onewingedsh...@gmail.com> wrote:
>
> > Sure, a child-package could be introduced to extend the object, but
> > its specification cannot rely on anything not publicly visible in its
> > parent's specification... meaning that the public portion of the
> > object cannot expose that it is a tagged record. Right?
>
> package X is
>
> =A0 type Final is private;
>
> private
>
> =A0 type Final is tagged null record;
>
> end X;
> package X.X is
>
> =A0 type Extended_Final is tagged private;
>
> private
>
> =A0 type Extended_Final is new Standard.X.Final with null record;
>
> end X.X;

Yes, but that is NOT exposing that FINAL is tagged, only that
Extended_Final is; moreover, since the definition of Extended_Final
[which extends FINAL] is in the private portion it cannot be relied
upon in the public portion of other specifications... (i.e. we are
free to change Extended_Final's implementation in any way we see fit
so long as it satisfies all its public specifications.)