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From: AdaMagica <christ-usch.grein@t-online.de>
Newsgroups: comp.lang.ada
Subject: Re: Will "renames" increase program size?
Date: Wed, 15 Jun 2011 23:59:35 -0700 (PDT)
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Date: 2011-06-15T23:59:35-07:00
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On 15 Jun., 15:15, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Wed, 15 Jun 2011 13:24:52 +0200, Yannick Duch=C3=AAne (Hibou57) wrote:
> > Le Wed, 15 Jun 2011 07:37:22 +0200, Randy Brukardt <ra...@rrsoftware.co=
m> =C2=A0
> > a =C3=A9crit:
> >> Some examples where there probably would be some overhead:
>
> >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0Obj : Natural renames =
My_Array (Some_Variable).all;
> >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0Obj2 : Float renames S=
ome_Function (A, B);
>
> > Yes, because this is more an aliasing (in the symbolic sense) than a =
=C2=A0
> > proper renaming.
>
> Yes, Ada's renaming is not renaming. Consider this:
>
> =C2=A0 =C2=A0Line : String renames Get_Line;
>
> It calls Get_Line once and keeps the result object. In fact it is an
> equivalent to:
>
> =C2=A0 =C2=A0<anonymous> : constant String :=3D Get_Line;
> =C2=A0 =C2=A0Line : properly renames <anonymous>;
>
> Consider also the effect of renaming on the visibility rules:
>
> =C2=A0 =C2=A0package P1 is
> =C2=A0 =C2=A0 =C2=A0 End_Error : exception renames Ada.Text_IO.End_Error;
> =C2=A0 =C2=A0end P1;
> =C2=A0 =C2=A0package P2 is
> =C2=A0 =C2=A0 =C2=A0 End_Error : exception renames Ada.Text_IO.End_Error;
> =C2=A0 =C2=A0end P2;
> =C2=A0 =C2=A0use P1, P2;
>
> =C2=A0 =C2=A0exception
> =C2=A0 =C2=A0 =C2=A0 when End_Error =3D> -- End_Error is hidden!
>
> Ada's "renames" does not rename here, it copies, creates objects. There a=
re
> three End_Error here, all of them are equal, but not same:
>
> exception
> =C2=A0 =C2=A0when Ada.Text_IO.End_Error =3D>
> =C2=A0 =C2=A0 =C2=A0 ...
> =C2=A0 =C2=A0when P1.End_Error =3D> -- Error! P1.End_Error has the same v=
alue
> =C2=A0 =C2=A0 =C2=A0 ...
> =C2=A0 =C2=A0when P2.End_Error =3D>
> =C2=A0 =C2=A0 =C2=A0 ...
>
> A proper renaming would create identical (x=E2=89=A1y) entities, Ada's re=
naming
> sometimes creates only equal ones (x=3Dy).
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de

That's not correct. A renaming does not copy nor somehow create new
entities, it only creates new names for the same thing. Since
visibility is via names, you arrive at unresolvability issues.