Re: Will "renames" increase program size?

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

On Wed, 15 Jun 2011 13:24:52 +0200, Yannick Duchêne (Hibou57) wrote:

> Le Wed, 15 Jun 2011 07:37:22 +0200, Randy Brukardt <randy@rrsoftware.com>  
> a écrit:
>> Some examples where there probably would be some overhead:
>>
>>              Obj : Natural renames My_Array (Some_Variable).all;
>>              Obj2 : Float renames Some_Function (A, B);
>>
> Yes, because this is more an aliasing (in the symbolic sense) than a  
> proper renaming.

Yes, Ada's renaming is not renaming. Consider this:

   Line : String renames Get_Line;

It calls Get_Line once and keeps the result object. In fact it is an
equivalent to:

   <anonymous> : constant String := Get_Line;
   Line : properly renames <anonymous>;

Consider also the effect of renaming on the visibility rules:

   package P1 is
      End_Error : exception renames Ada.Text_IO.End_Error;
   end P1;
   package P2 is
      End_Error : exception renames Ada.Text_IO.End_Error;
   end P2;
   use P1, P2;
   
   exception
      when End_Error => -- End_Error is hidden!

Ada's "renames" does not rename here, it copies, creates objects. There are
three End_Error here, all of them are equal, but not same:

exception
   when Ada.Text_IO.End_Error =>
      ...
   when P1.End_Error => -- Error! P1.End_Error has the same value
      ...
   when P2.End_Error =>
      ...

A proper renaming would create identical (x≡y) entities, Ada's renaming
sometimes creates only equal ones (x=y).

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