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From: john.mccabe@emrad.com.nospam (John McCabe)
Newsgroups: comp.lang.ada
Subject: Re: on package naming, should the word "_pkg" be part of it?
Date: Wed, 10 Oct 2001 13:05:09 GMT
Organization: Emrad Ltd
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Date: 2001-10-10T13:05:09+00:00
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On 9 Oct 2001 18:48:24 -0700, Robert*@ <Robert_member@newsguy.com>
wrote:

>I wish the Ada95 designers would have introduced the class construct as in

Me too but why not just:

Class XXX is
   ...

etc?

The package mechanism had been in place for over 10 years as a method
if encapsulation and so on. While I can see that the use of tagged
types is an impressively versatile means of implementing OO features,
I have found that, where OO implementations are required, the 'class'
is generally mimicked by using a package with a single tagged type and
its primitive operations.

So instead of:

package XXXs is
   type XXX is abstract tagged null record;
   procedure DoSomething (This : in XXX);
   procedure AClassOperation;
end XXXs;

package YYYs is
   type YYY is new XXX with
      record
         Item_1 : Integer;
      end record;
   ClassItem : Integer;
end YYYs;

why not have something like:

class XXX is
   procedure DoSomething;
   procedure AClassOperation is classwide;
end XXX;

class YYY extends XXX is
   procedure DoSomething;
   Item_1 : Integer;
   ClassItem : Integer is classwide; -- Use classwide, not static!!!
end YYY;

So essentially a 'class' is just a package with an implicit tagged
type. Surely this must have been considered, I mean, you could even
write your classes like this and easily parse it into a package with a
tagged type!


Also, having worked with a number of people on Ada projects who had
recently used Java, C++, Visual Basic etc, I think the lack of an
object.method syntax was a serious limitation to their acceptance of
Ada 95 as an OO language.