Re: Dynamic type system for Ada

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

On 24/01/2017 22:21, Randy Brukardt wrote:

> I do wonder how useful such a hierarchy would be, but I suppose someone
> would have to build it to find out.

Not much. I did exactly this before.

The problem is that you get the "god-class" in the end. In order to be 
able to re-interpret the value as a given scalar type you have to add a 
primitive operation to the abstract base. E.g.

    function As_Unsigned_32 (Value : Abstract_Variable)
       return Unsigned_32 is abstract;
          -- Raises Type_Error if not of the type

And so for each scalar type. And for arrays and records.

Otherwise you have to explicitly convert (upcast) to specific instance 
derived from Abstract_Variable which is much worse.

P.S. I intended to use that on top of a stream exchange, but the 
interface is so heavy that it adds no advantage to direct reading the 
target object from the stream.

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