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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: In precision typing we trust
Date: Fri, 29 Aug 2025 10:07:45 +0200
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On 2025-08-29 05:53, Lawrence D’Oliveiro wrote:

> But they are still of that same “Abstract_Packet'Class”, which is the base
> class.

Yes, because it was designed so. This is what being typed is.

> You cannot specify “Foo_Packet'Class” as the return type on one
> call, “Bar_Packet'Class” on another call, etc.

Why should I? The return type is equivalent (not is!) to Foo_Packet in 
one call and Bar_Packet in another.

A value of Abstract_Packet'Class can be viewed as a value of Foo_Packet, 
if the type tag specifies Foo_Packet as the specific type. You can check 
the tag dynamically or use it indirectly in dispatching calls = calls to 
methods (in Ada terminology "primitive operations").

The caller expects a value of a class member = a value of a descendant 
of Abstract_Packet.

This paradigm in literature is called "generic programming" when a 
program is written in terms of a class (class Abstract_Packet) = a set 
of types derived from Abstract_Packet = {Foo_Packet, Bar_Packet, ...}. 
The program does not know the specific type and need not to know.

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