Why don't implement a circular list so that  <last element>.Next accesses to
List.Start.

Lutz Donnerhacke <lutz@iks-jena.de> escribi� en el mensaje de noticias
slrn8j9hrm.mk.lutz@taranis.iks-jena.de...
> I run into a problem with my list_mixin.
>   ftp://ftp.iks-jena.de/pub/mitarb/lutz/ada/types/list_mixin.ad?
>
> generic
>    type Base (<>) is abstract tagged limited private;
>    type S    (<>) is abstract new Base with private;
> package List_Mixin is
>    type T is abstract new S with private;
>    type T_Class is access all T'Class;
>    type List is limited private;
>    -- several lines of code deleted
> private
>    type T is abstract new S with
>       record
>          Next : T_Class := null;
>          Used : Boolean := False;  -- to detect multiple insertions
>       end record;
>
>    type List is limited
>       record
>          Start : T_Class := null;
>       end record;
>    -- several lines of code deleted
> end List_Mixin;
>
> The current implementation use null at the tail marker. This requires the
> flag Used and causes a lot of ineffient code.
>
> So I'd like to introduce a single fixed end node used by all
instantiations.
> It should contain only the Next element.
>
> How can I achieve it?
>
> Using assembly I added the link in front of the structure and ignored the
> varying context following it. Good examples can be found in D.E.Knuth
TAoCP.