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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: newbie - OOP in Ada Set and Get Methods
Date: Tue, 28 Dec 2004 19:58:38 +0000 (UTC)
Organization: GMUGHDU
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Date: 2004-12-28T19:58:38+00:00
List-Id: <comp.lang.ada>

R <ruthless@poczta.onet.pl> wrote:
: because all OOP languages uses references to pass the objects as
: parameters...

Ada may or may not use references depending on what kind of
value a subprogram parameter takes. But for tagged types, passing
values is always by reference, no need for an explicit pointer.

Object construction is slightly different in Ada, I think.
The function approach is one way to do it.
I liked this discussion:
http://www.cmis.brighton.ac.uk/staff/je/adacraft/ch14.htm
http://www.cmis.brighton.ac.uk/staff/je/adacraft/ch15.htm

You can also use a constructor procedure.
For example,

package Test_Class is

   type Rec_1 is tagged
     record
       value: Integer;
     end record;

   procedure make(r: in out Rec_1; .......);
   -- initialises all components of `r`


   function get(r: Rec_1) return Integer;

   procedure set(r: in out Rec_1; v: Integer);

end Test_Class;


Then somewhere else in your program,

declare
   x: Rec_1;
begin
   make(x, .......);
   set(x, 5);
   get(x);
end;

You could also have automatic initialisation using
default values for the object's components,

   type Rec_1 is tagged record
     value: Integer := default_value;
   end record;

One more thing: Ada allows nesting blocks. So in many
cases, you can combine these techniques (and more).
Note that `default_value` can be a function.


-- Georg