Re: Ada 95 and Class attribute for none-tagged incomplete type

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

On Mon, 3 Aug 2009 08:26:24 -0700 (PDT), Adam Beneschan wrote:

> Keep in mind that this isn't a privacy issue.  The main reason for
> incomplete types is so that you can declare linked lists and things
> like that.  Allowing a 'Class reference to a type not yet declared as
> tagged allowed things like this:
> 
>    type Rec;
>    type Rec_Acc is access all Rec'Class;
>    type Rec is tagged record
>        ...
>        Next : Rec_Acc;
>    end record;
> 
> so that you could have a heterogeneous list of records.

Well, I would argue that logically the above could be rather:

   type Rec;
   type Rec_Acc is access all Rec;
   type Rec'Root is tagged record
       ...
      Next : Rec_Acc;
   end record;

Here 'Root is defined so that T'Class'Root = T. So Rec is class-wide.

Of course, from the stand point that any type has a class rooted in it,
Rec'Class is fully OK. But if we wanted further to pretend that some types
are more "classy" than others, we could maintain such distinction in a way
like above.

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