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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: derived formal types and known discriminants
Date: Fri, 30 Jun 2017 13:09:58 -0500
Organization: JSA Research & Innovation
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Date: 2017-06-30T13:09:58-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:oj4ubr$190j$1@gioia.aioe.org...
> On 30/06/2017 03:10, Randy Brukardt wrote:
>
>> Surely, but no real loss. Using discriminants with tagged types is pretty
>> rare in itself.
>
> Access discriminants are needed to work around lack of constructors and 
> full multiple inheritance. That is when one object refers to its separate 
> part via an access discriminant.

Possibly, but that seems hard to work with. And as someone that rarely sees 
the value of inheritance in the first place, I doubt I would bother trying. 
YMMV.

> Value discriminants are needed for having components of unconstrained 
> types.

Sure, but they're very inflexible in that usage (as bad or worse than the 
original unconstrained types). So I tend to view these as an either/or 
proposition: untagged, mutable types with discriminants, or tagged types 
without discriminants. Again, YMMV.

                   Randy.