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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Best use cases for OOP (resent quoted sorry)
Date: Fri, 29 Aug 2025 10:28:24 +0200
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On 2025-08-28 22:23, Alex // nytpu wrote:

> The only 
> real issue is that IIRC tagged types are always at least twenty bytes on 
> GNAT (on ARMv4T/ARMv5T at least, since developing for them is the only 
> time I've gotten warnings about this limitation) which precludes things 
> like having a record be small enough to be passed in a register instead 
> of the stack, but not much of an issue on modern systems.

The reason is that tagged types are by-reference types. And that is 
because one wanted to have T'Class <-> T conversions a mere view 
conversions.

One language extension I always wanted were an ability to have classes 
of types without having a tag embedded in the representation. So that 
one could have Boolean'Class. In this model T'Class <-> T would be a 
full conversion producing a new object. The types must be by-value then. 
Furthermore for such types re-dispatch would be impossible:

    procedure Foo (X : in out T) is
    begin
       T'Class (X).Bar; -- Error, T'Class (X) is a new object

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de