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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Tue, 19 Mar 2013 21:45:23 +0100
Organization: cbb software GmbH
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Date: 2013-03-19T21:45:23+01:00
List-Id: <comp.lang.ada>

On Tue, 19 Mar 2013 21:07:18 +0100, J-P. Rosen wrote:

> Le 19/03/2013 18:31, Dmitry A. Kazakov a �crit :
>> Subtype is a type that inherits some operations (interface) of another
>> type, called "parent type," "base type," "ancestor type" or "supertype."
> 
> This may be the source of the confusion. What you describe is called
> "subtype" in other languages, but this is called "derived type" in Ada.
> An Ada subtype is a completely different beast, that does not correspond
> to this definition.

And how is it different?

> And please, bear in mind that other languages do not have anything
> similar to Ada subtypes, therefore you cannot compare Ada subtypes to
> features of other languages.

Practically all languages have subtypes which share the representation of
the parent while adding a constraint. E.g. const T in C++ is such a
subtype.

Of course insistence on keeping the representation erodes the principle of
separation interface and implementation. Ada would be much better off if
all derived types could change the representation like arrays do when
constrained.

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