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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Getting the index for an element in mutually referencing
 containers
Date: Mon, 13 Mar 2017 14:55:09 -0500
Organization: JSA Research & Innovation
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Date: 2017-03-13T14:55:09-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:oa41a4$1ko5$1@gioia.aioe.org...
> On 2017-03-12 17:44, Simon Wright wrote:
...
> P.S. It is a pity that Implicit_Dereference type does not have proper 
> interface to work with *any* type instead of discriminated records. This 
> is design fault when the use case #2 was taken for #1.

It works with any type, since the real target type is the thing designated 
by the discriminant. The discriminant is the key, because it is the only way 
in Ada to get an access type with a controlled lifetime. The discriminated 
type is just a helper, not the end result.

Yes, we could have done that some other way, and indeed we started with a 
separate construct, but the semantics ended up identical to that of an 
access discriminant of a controlled type -- so why build another construct 
(with all of the additional chances of getting it wrong) when an existing 
one will do? Syntax sugar covers up the mess in almost all uses - and that's 
a lot easier to define correctly.

                                                   Randy.