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From: Ken Garlington <garlingtonke@lmtas.lmco.com>
Subject: Re: Ada95 OOP Questions
Date: 1996/07/30
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Date: 1996-07-30T00:00:00+00:00
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Spasmo wrote:

> Well here's the thing though, from what I'm seeing when you
> use the package you'd need to pass the parameters to the
> subprograms rather than having the data encapsulated.  For
> instance in C++ you'd do the following:
> 
>         Person p;
>         p.walk();
>         p.talk();
>         p.eat();
> 
> But with the above you'd do something like the following:
> (Any Ada code provided may be slightly erroneous, I just want
> to give a general idea of what I think I understand hence not
> checking much).
> 
> with Persons;
> 
> procedure Main is
> 
>         P : Persons.Person;
> 
> begin
>         Persons.Walk(P);
>         Persons.Talk(P);
>         Persons.Eat(P);
> end Main;
> 
> Correct me if I'm wrong on this.  So you're still passing parameters
> which means that data and subprograms are still 2 different entities
> which sorta hurts the abstraction, rather than in say C++ where
> you've got a unified object.

Depends on what you're abstrating. If you don't want an abstract data type,
but you want a generic abstract data object, why not do this:

  generic
  package Person is

    procedure Walk;
    procedure Talk;
    procedure Eat;

  private

    type Person_Type is -- as before
    Object : Person_Type;

  end Person;

Translating your C++ code:

   package P is new Person;  -- Person p;
   P.Walk;                   -- p.walk();
   P.Talk;                   -- p.talk();
   P.Eat;                    -- p.eat();

Note, however, that there are things you can't do with a GADO (like
make an array of Persons) that you can do with an ADT.

If your complaint is that you like p.eat() better than eat(p), on the
other hand, then I don't see this as an abstraction difference - just
a syntax difference.

Just out of curiousity, if Person is declared in the C++ equivalent of
a package (and I forget the nomenclature -- space?), what does your C++
code look like?

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