Re: APQ

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

On Wed, 22 Dec 2004 10:29:01 +1100, Brian May wrote:

>>>>>> "Dmitry" == Dmitry A Kazakov <mailbox@dmitry-kazakov.de> writes:

>     Dmitry> function Copy (C : Root_Connection_Type)
>     Dmitry> return Root_Connection_Ptr is abstract;
> 
>     Dmitry> This would allocate a copy and connect it to the same
>     Dmitry> DB. Because reference counting is intended you will need
>     Dmitry> dynamic allocation anyway. The user will of course do it
>     Dmitry> all with handles:
> 
> I have a suspicion this would not work as Root_Connection_Type is a
> limited type. Or am I yet again mistaken?

You probably mean this:

   function Copy (C : Root_Connection_Type'Class)
      return Root_Connection_Ptr is
   begin
      return new Root_Connection_Type'Class'(C);
   end Copy;

This indeed cannot work for limited types. This was the reason why Copy was
declared abstract primitive instead:

   function Copy (C : Root_Connection_Type)
      return Root_Connection_Ptr is abstract;

It will dispatch to an implementation which knows how to copy itself:

   function Copy (C : My_Connection_Type)
      return Root_Connection_Ptr is
      Result : Root_Connection_Ptr := new My_Connection_Type;
      Object : My_Connection_Type renames My_Connection_Type (Result.all);
   begin
      Object.Field_Foo := C.Field_Foo;
      ... -- Clone me tender
      return Result;
   exception
      when others =>
         Free (Result); -- No memory leaks!
         raise;
   end Copy;

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