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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Legit Warnings or not
Date: Mon, 8 Aug 2011 16:30:16 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2011-08-08T16:30:16-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:fopu9zln3g4f.1ocdgf28k7s69.dlg@40tude.net...
> On Fri, 5 Aug 2011 18:57:43 -0500, Randy Brukardt wrote:
...
>> I don't see any implicit constraints. If there are any, they ought to be
>> eliminated.
>
> Then:
>
>   procedure Carcinogenic (X : in out T'Class) is
>      Y : T;
>   begin
>      X := T;
>   end Carcinogenic;
>
>   Z : S'Class; -- Constrained to S'Class?
> begin
>   Carcinogenic (T'Class (Z)); -- Ignore the constraint!
>
> [ Your idea is to make all classes subtypes of some huge dynamic type. 
> This
> is not a workable type model as so many OOPLs already showed. ]

As I said, there shouldn't be any partial constraints. But S'Class is not a 
constraint, it is a type. The problem here is that the type system is being 
violated by back conversion of Z from the less restrictive type. So I think 
this conversion should be illegal.

However, I have to agree that such a rule would be too incompatible for Ada. 
So we'll have to forget my idea.

Unfortunately, I think this proves that we've pretty much taken the core of 
Ada as far as it can go. (We can still add stuff around the edges, as with 
the contracts.) If we really want to advance, we're going to have to start 
over.

                               Randy.