Re: Self-referential types

["Vladimir Olensky" <vladimir_olensky@yahoo.com>]

Ted Dennison wrote in message <7ttb4a$8mq$1@nnrp1.deja.com>...
>I'm trying to create my first self referential type. But there's
>obviously something about this technique I'm missing, because all
>attempts produce compiler errors in multiple compilers.
>
>Below is a code sample that is taken directly from Cohen's AAASL,
>section 11.8.3:
>
>procedure Test is
>
>   type Cell_Type;
>
>   type List_Type is access all Cell_Type;
>
>   type Cell_Type is
>     limited record
>        Contents_Part      : String (1..20);
>        Next_Cell_Part     : List_Type := Cell_Type'Access;
>        Previous_Cell_Part : List_Type := Cell_Type'Access;
>     end record;
>begin
>   null;
>end Test;




It seems that this example  was not tested.

How it is  possible to initialize access variable
by the initial value that is access attribute to type ?
Access attributes can not be applied to type.
It may only be  applied to some object but not to its description.

Also compiles are probably giving  misleading error messages.

If you change your example to:
-------------------------------------
Procedure Test is
    type Cell_Type;
    type List_Type is access all Cell_Type;

    type Cell_Type is    limited record
        Contents_Part : String (1..20);
        Next_Cell_Part : List_Type := null;
        Previous_Cell_Part : List_Type := null;
    end record;

 Wrong_Initialization : List_Type := Cell_Type'Access;

begin
    null;
end Test;
------------------------------------------
than you will have right error message regarding
Wrong_Initialization  varible:

>>>test.adb:14:37: "Access" attribute cannot be applied to type
gnatmake: "test.adb" compilation error

Regards,
Vladimir Olensky