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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada Successor Language
Date: Mon, 25 Jun 2018 22:16:33 +0300
Organization: Tidorum Ltd
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Xref: reader02.eternal-september.org comp.lang.ada:53310
Date: 2018-06-25T22:16:33+03:00
List-Id: <comp.lang.ada>

On 18-06-25 17:21 , Dmitry A. Kazakov wrote:
> On 2018-06-25 16:03, Niklas Holsti wrote:
>
>> (In fact, it seems to me that Ada could allow untagged record
>> extensions as well; the effect would be the same as for tagged ones,
>> but no 'Class would be formed, and no class-wide programming or
>> dynamic dispatch could be used, so all such types would be static.
>
> Ada could allow T'Class for untagged T. T'Class would be an indefinite
> type with values consisting of the actual type's tag and its value. When
> T is by-value type, you pass T'Class to a subprogram as tag + value.
> When T is by-reference type, you pass tag + reference.

Yes, that could be another point in the division of the "OO programming 
concept" into smaller, more "primitive" features -- building blocks -- 
which could be combined in various ways.

Your suggestion would allow class-wide programming without storing tags 
_in_ objects.

> Upon dispatch, you strip the tag from the value or reference before
> passing value/reference down.

> P.S. No re-dispatch is possible in this model, sorry.

Indeed. However, while I insist on re-dispatch in some cases, I don't 
insist on re-dispatch in all cases :-)  The possible need for 
re-dispatch would then be one of the reasons for choosing the untagged 
approach (your suggestion) or the tagged approach (present Ada).

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .