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Subject: Re: A bad counterintuitive behaviour of Ada about OO
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Date: 2014-08-08T02:34:43-06:00
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On 08-Aug-14 01:54, Maciej Sobczak wrote:
> W dniu czwartek, 7 sierpnia 2014 10:50:52 UTC+2 użytkownik Dmitry A. Kazakov napisał:
>
>>> and no support for type covariance on return
>>> type Ada is way more broken than other languages I am aware of.
>>
>> I don't understand this. The return type is covariant in Ada.
>
> Can I have Better_Factory type with a primitive operation returning Better_Product?
>
> No, because Better_Product is a different type than Product and such operation
> would not be considered overriding. This works properly in just about any other
> language with support for OO.
>

Can't you use some class-wide functions, some primitive functions, and 
the Generic_Dispatching_Constructor function to do this?

IIRC something like:

   Type Base is abstract tagged null record;
   Function Product return Base is abstract; -- Primitive function.
   Function Get_Product return Base'Class;   -- Dispatches call to Product.
   -- Uses generic_dispatching constructor.
   Function Make(Stream : not null access
                          Ada.Streams.Root_Stream_Type'Class)
         return Base'Class;                  -- For Stream-creation.
   -- Perhaps some other creation functions.
   -- ...

   Type Child is tagged ...

Or am I misunderstanding you?