Re: Writing an Operating System in Ada

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

On Mon, 18 Jan 2010 12:23:23 +0100, Georg Bauhaus wrote:

> If there is a misunderstanding, please help:
> in a world of existing separate OSs, or of to be
> designed OSs, would their respective persistence layers allow,
> given the identifier of some object,

Identifier of some object = the object itself, like when you write in Ada:

    X : Integer;

X is the object and an identifier of.
 
> (1) calling primitive subs defined with the object's type T

Certainly.
 
> (2) learning about T's subs in case the object was stored
>     by some program (defining T) not known to the caller,

No, you don't have the object then (object = identity + type + value).
First you have to convert the type of the object and get a view or else
another transient object of the desired type. Ada's equivalent:

   X : T'Class;
begin
   ... S (X) ...  -- S is a member of T'Class

You might also be able to check if X in S'Class etc.

> (3) adding subs to T to accomodate specified processing needs
>     of another, later program? How?

By conversion of the object to another type:

   X : Integer;
   Y : Float := Float (X); -- Now we have sin, cos etc

This conversion might happen to be a view conversion or not.

1,2,3 represent no problem. IMO the real challenge (apart from consistent
implementations of MI and MD) are dynamic types marshaled between the parts
of a distributed system. I didn't think much about that, so don't expect me
to answer how that should be solved. Probably others might have some
insights...

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