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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Ada OO Mechanism
Date: 1999/06/14
Message-ID: <wccpv2yzmmw.fsf@world.std.com>#1/1
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Sender: bobduff@world.std.com (Robert A Duff)
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Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1999-06-14T00:00:00+00:00
List-Id: <comp.lang.ada>

Brian Rogoff <bpr@shell5.ba.best.com> writes:

> Yes, I know. I can understand why it makes sense that a record cannot 
> contain unconstrained types, but I don't understand why a suitable 
> generalization of Ada's ability to return unconstrained types could not be 
> made to solve the problem being discussed *without* forcing a heap based
> mechanism on Ada. An example might be returning two strings on the stack.

Well, you can return two strings on the stack by returning a record that
looks like this:

    type String_Pair(Length1, Length2: natural) is
        record
            String1: String(1..Length1);
            String2: String(1..Length2);
        end record;

But you can't do that with class-wide, because there's no constraint to
constrain the tag of an object, analogous to the constraints on the
upper bounds of the above strings.  Adding such a concept to the
language would add functionality, but would also add complexity.
Probably not worth it.

- Bob
-- 
Change robert to bob to get my real email address.  Sorry.