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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: A question for my personal knowledge.
Date: 1999/05/15
Message-ID: <m3ogjnorwv.fsf@mheaney.ni.net>#1/1
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References: <1VEZ2.1515$I51.88140@carnaval.risq.qc.ca>
 <37372A84.641F2133@bigfoot.com> <7h8oe8$2js$1@cf01.edf.fr>
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 <7h9pei$aut$1@nnrp1.deja.com> <373AC668.4824FF07@decada.enet.dec.com>
 <7hfctj$1kb4@drn.newsguy.com>
 <dale-1405990852190001@r1021c-34.ppp.cs.rmit.edu.au>
 <7hfp1n$28tr@drn.newsguy.com>
NNTP-Posting-Date: Fri, 14 May 1999 21:48:06 PDT
Newsgroups: comp.lang.ada
Date: 1999-05-15T00:00:00+00:00
List-Id: <comp.lang.ada>

Mike  <Mike@newsguy.com> writes:

> In Ada, you still use function calls and pass tagged records as
> parameters.
> 
> in real OO, you invoke methods on objects.

You are confusing syntax and semantics.  The call

  Push (X, On => Stack);

really does "invoke a method on an object."  


> Also, a class is more clear representation of an object. in Ada, bolting
> OO concepts into a procedural language, makes the way to do OO in Ada
> not very natural at all.

Ada83 was already a class-based language.  All Ada95 was to extend the
existing facilities for class-based programming with type extension.

In Ada83, you did this:

  type T is private;


In Ada95, you do this:

  type T is tagged private;


In Ada83, you did this:

  type NT is new T;

In Ada95, you do this:

  type NT is new T with private;


What's "bolt-on" about that?  Ada95 was designed specifically to NOT add
bolt-on features, so your statement to the contrary is incorrect.

 
> The biggest mistake Ada made in 95 was not introduce the class
> construct as is common in other OO languages.  Who cares if that would
> have broken Ada83 programs, you could have called it X95 for all I
> care, it did not have to be called Ada.

But the class already existed in Ada83: it's called a "private type".

  type Stack_Type is private;

  procedure Push
    (Item : in     Item_Type;
     On   : in out Stack_Type);

  function Get_Top (Stack : Stack_Type) return Item_Type;


In Ada95, I might say:

  type Stack_Type is tagged private;

  procedure Push
    (Item : in     Item_Type;
     On   : in out Stack_Type);

  function Get_Top (Stack : Stack_Type) return Item_Type;


Not much difference, except that in Ada95 I can extend the stack type:

  type My_Special_Stack is new Stack_Type with private;



> sorry, but OO in Ada is not normal OO. I am happy that you have no problem
> with it, but 99% of the rest of the world do not do OO that way Ada does it.

You seem not to understand the difference between syntax and semantics.