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From: pitre@n5160d.nrl.navy.mil (Richard Pitre)
Subject: Re: Real OO
Date: 1996/03/15
Message-ID: <4icdmc$fef@ra.nrl.navy.mil>#1/1
X-Deja-AN: 142910779
references: <DoBH80.9u9@world.std.com>
organization: Naval Research Laboratory
newsgroups: comp.lang.ada
Date: 1996-03-15T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <DoBH80.9u9@world.std.com> bobduff@world.std.com (Robert A Duff)  
writes:
> In article <DoArzG.7v1@assip.csasyd.oz>,
> Don Harrison <donh@syd.csa.com.au> wrote:
> >Although such basic types are not explicitly defined as classes in Ada,
> >they are effectively classes because their features are 'inherited'
> >through subtyping and derivation. You wouldn't want to define '+' for
> >every arithmetic abstraction.
> 
> Just to clarify, Ada *does* use the term "class" to refer to the set of
> all integer types, for example.  And you are correct that you get
> inheritance for these classes -- both for predefined things like '+' and
> for user-defined operations.  However, you do not get type extension
> (you can't add new fields to an integer type when you derive from it),
> and you do not get polymorphism.
> 
> - Bob

I'm just learning Ada and I don't understand what you mean by "can't add new  
fields ...". Does this mean that when you subclass a built in integer type that  
you can only add new methods but no new instance variables? 

richard