Mixin with preelaborated element

Mixin with preelaborated element

[Lutz Donnerhacke]

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.

RE: Mixin with preelaborated element

[Antonio Dur�n Dom�nguez]

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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.

Re: Mixin with preelaborated element

[Lutz Donnerhacke]

* Antonio Dur�n Dom�nguez wrote:
>Why don't implement a circular list so that  <last element>.Next accesses to
>List.Start.

I'm looking for a solution, not a workaround. A circular list does indeed
exists in my lib, but it offers an extended interface. I'd like to choose an
implementation based on the needs of the algorithm not based on the
(in)flexibility of the programming language.

BTW: Even a circular list has the same problem: How to provide a base node.