Dynamic Instantiation in Ada95 ?

[Matthias Oltmanns <Matthias.Oltmanns@SO.SEMA.DE>]

Hi all,

I would like to implement a kind of runtime instantiation for class-wide
types, where the concrete type is not known
at compile time.
I've searched for a method in exact that way as S'Class'Input is working.
S'Class'Input first reads the external tag name from a stream and than
makes a dispatching call to the appropriate S'Input method.

Example:
...
    type Base is tagged with null record;

    function Create return Base;
    --
    function Create_Dynamic (Tag_Name : String) return Base'Class;
 ...
   << Some type-extensions for the type Base >>
...

I would like to implement the function as follows:

   function Create_Dynamic (Tag_Name : String) return Base'Class is
     T : Ada.Tags.Tag := Ada.Tags.Internal_Tag (Tag_Name);
    begin
        return <<dispatching call to Create using tag T>>;
    end Create_Dynamic;

Is there a way to do that? I've found only some dirty hacks, using
unchecked_deallocation , for T'Address use ...
and so on.

I'am interresting for a more portable approach. Any suggestions?

Matthias Oltmanns,  Email: Matthias.Oltmanns@so.sema.de, Phone: +49 4421
802 207, Fax: +49 4421 802 444,
SEMA GROUP GmbH Wilhelmshaven (Germany) - Special Systems Division -