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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Access to function returning class-wide type
Newsgroups: comp.lang.ada
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Date: Thu, 21 Aug 2008 13:02:40 +0200
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Date: 2008-08-21T13:02:43+02:00
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On Thu, 21 Aug 2008 12:13:10 +0200, Pawe� 'Nivertius' P�azie�ski wrote:

> What I need is a access type to 'constructor' of an derivate of abstract
> object.
> As I presented, there is a workaround, but that's not the 'right' way to do
> it. I really want to do it without some tricky wrapping.
> How do I define The_Access_Type to do what I want?

See Ada.Tags.Generic_Dispatching_Constructor. It gives you a function
constructing an object from the type tag, the parameters (Natural in your
case) using the function you want (Proc). It goes as follows:

with Ada.Tags.Generic_Dispatching_Constructor;
package A is 
   type Abstracted is abstract tagged null record;
   function Proc (N : not null access Natural)
      return Abstracted is abstract;
   function Constructor is
      new Ada.Tags.Generic_Dispatching_Constructor
             (Abstracted, Natural, Proc);
end A;

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