Re: Virtual Components in Ada and Ruby

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

On Thu, 30 Jun 2005 13:55:18 -0500, Randy Brukardt wrote:

> But the whole idea seems misguided to me - programs shouldn't be exporting
> components [including discriminants] (virtual or otherwise) in the first
> place. All of that should be hidden with a set of operations to access them,
> construct them, and the like.

So the set of operations in this case is (simplified) ".<name>" and
".<name>:=". The point is that there must be a better separation of
implementation and interface. Why something publicly declared as a tagged
record cannot be implemented using an access type?

> Ada 200Y certainly has made that easier by
> giving real constructors to limited types, so there should no longer be any
> reason to expose any components.
>
> As always, I can think of a handful of exceptions to the rule (just like
> there are a few types that probably shouldn't be tagged and derived from
> Controlled or Limited_Controlled), but there aren't enough of these to
> justify any additional language features.

It is not an additional feature in my view. It is less features, though
also a structural language reform. I'd like to remove predefined types
classes as much as possible.
 
> There's a better argument for a virtual array capability, because that has
> properties that are tough to emulate with subprograms. But even that's
> questionable (especially in face of the difficulties of defining and
> implementing slices and aggregates for such things).

Right. Slices and aggregates must become first-class citizens, first.

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