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From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: oo programing question
Date: Sun, 07 Dec 2003 15:01:23 +0100
Organization: AdaCL
Message-ID: <4445978.xFQpVZx21n@linux1.krischik.com>
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shoko wrote:

> i have the following code:
> 
> package a is
>   --car class --
>   type a is tagged private;

There are two schools here:

1. Packages are multiples and objects are singles:

package Cars is
type Car is ...

2. Packages are singles and objects are Object:

Package Car is
type Object is

Calling the Type the same as the package gets you into trouble when code
becomes more complex.

>   type a_ptr is access all car'class;

Use "access" and not "access all" whenever possible.
   
> with a;
> 
> package b is
>    type b is new a.a with private;   <--  constraint error
>    type b_Ptr is access all b'Class;
> 
>    function init_b(maximum:positive) return b_Ptr;

Are you shure you need a access here? Adas stack handling is far more
powerfull then C++'s. So you might be better of just to return 'b'. Look at
New_Object in

http://adacl.sourceforge.net/html
______Include__AdaCL-SAR-Filter-Replace__adb.htm


>   private
>      type b is new  a.awith
>      record
>          maximum_:positive;
>      end record;
> end b;
> -------------------------------------------
> in the main procedure:
> 
> with a;use a;
> with b;use b;

don't "use" everything. 
 
> procedure main is
>    new_b:b_ptr;
>      
> begin
>     new_b := init_b(90);
>  end main;
> 
> i get constraint error on b.ads
> i dont understand why

Difficult without the package bodys.

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://adacl.sourceforge.net