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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Universal type in Ada
Newsgroups: comp.lang.ada
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Date: Thu, 16 Jun 2005 13:59:43 +0200
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Date: 2005-06-16T13:59:43+02:00
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On 16 Jun 2005 10:18:44 +0200, Ole-Hjalmar Kristensen wrote:

> Please do not do this. As someone (may have been John Max Skaller) on
> comp.lang.c++ said once, "casting is something you do when fishing".
> Think about what you are trying to do, and try to figure out how this
> can be accomplished by the tools available to you in Ada, like
> generics or run-time polymorphism.

Yes, but unfortunately, there is one case in Ada 95 where apparently
unnecessary downcasting is necessary: pool-specific access types to
class-wide objects:

type Object is tagged ...;
type Object_Ptr is access Object'Class;

function Create_My_Object (...) return Object_Ptr is
   Result  : Object_Ptr;
begin
   Result := new My_Object (...);
   declare
      This : My_Object renames  M_Object (Result.all);
         -- Casting is required because a pool-specific access
         -- to My_Object is not convertible to a pool-specific
         -- access to Object'Class!
   begin
      -- Do whatever needed to complete initialization of
      -- This
      ...
   end;
   return Result;
end Create_My_Object;

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