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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Suggestion: Allow functions returning abstract types in certain
 situations
Date: Sat, 24 May 2014 14:39:12 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2014-05-24T14:39:12-04:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Wed, 21 May 2014 19:19:21 -0400, Robert A Duff wrote:
>> Not sure what you mean about "redispatch".  You can't [re]dispatch
>> without converting to class-wide.
>
> Actually you can:
>
> 1. The Rosen's trick. You put a class-wide access discriminant into the
> abstract type and dispatch on it.
>
> 2. Consider:
>
>    type T is tagged ...;  -- Non-abstract
>    type S is abstract new T with ...; -- Abstract
>
> You convert to T, then that to T'Class and then dispatch on that. Never
> needed S'Class to make it crash.

Good points.  I still think it could work, given certain restrictions.
I should have said, "You can't [re]dispatch without obtaining a
class-wide view."  That's what would need to be prevented.

> Morale. Type semantics must be respected.

?

- Bob