Re: Proper program structure

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 30 Sep 2009 14:25:57 -0700 (PDT), Maciej Sobczak wrote:

> 2. Defining them in non-child packages means that they cannot see the
> complete structure of the Car and therefore they cannot be "wired" by
> discriminants like here:
> 
>    -- wrong:
>    type Car is limited record
>       Body : Body_Type (Car'Access);
>       Engine : Engire_Type (Car'Access);
>       -- and so on

They could with MI

   type Engine_Interface is limited interface;
---
   type Gear_Box_Interface is limited interface;
---
   type Engine_Type
      (  Gear_Box : not null access Gear_Box_Interface'Class
      )  is new Engine_Interface with ...
---
   type Gear_Box_Type is new Engine_Interface with ...
---

   type Car is
      new Ada.Finalization.Limited_Controlled
      and Engine_Interface
      and Gear_Box_Interface with private;

   private
      type Car is
         new Ada.Finalization.Limited_Controlled
         and Engine_Interface
         and Gear_Box_Interface with
      record
         Engine   : Engine_Type (Car'Access);
         Gear_Box : Gear_Box_Type;
      end record;

> Am I over-sensitive or did I really hit a design problem?

Yep, any design will ultimately collapse into dynamically typed mess on
further constraints like the engines of the class E_123'Class require gear
boxes from the class G_M25_X'Class.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de