Re: Is this expected behavior or not

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

On Fri, 22 Mar 2013 16:05:47 -0700 (PDT), Shark8 wrote:

> On Friday, March 22, 2013 4:18:02 PM UTC-6, J-P. Rosen wrote:
>> Le 22/03/2013 15:54, Dmitry A. Kazakov a �crit :
>> 
>>>> > Therefore,
>>>> > you can't translate Ada's subtypes into the terms of ADT.
>>> I just did it.
>> 
>> And that's where everybody (including those who designed/maintain the
>> language) thinks you are wrong.
> 
> I think I can see Dmitry's point but, like you said earlier, it's a matter
> of definitions

Then there should an alternative definition of ADT...

> So the problem is in the conflation of "values" and "valid values" of some [sub]type.

The problem is that subset is a set. So valid values are simply values of
Positive.

If you don't change the definition of ADT, Positive will keep on being ADT.

> That all is, IMO, a problem exacerbated in CS by the overpowering
> prevalence of "extension" in the "Object Oriented" paradigm; this even to
> the point that some of the new CS graduates [superficially] seem utterly
> unable to grasp the usefulness/utility of excluding values.

Right. The litmus test is to ask somebody who does not know Ada, isn't C's
int a class (type). This would produce no less fume as Positive vs. ADT.

It is a pity that Ada community keeps on insisting on this on their side of
the wall, refusing to see that either subtype or tagged type, they are just
different ways of creating a new type from existing ones, while having a
type for objects accommodating values of both ancestor and predecessor
types.

There is no reason why derived types shall always be extensions. It is an
*implementation* detail. Ada people should knew better about separation of
interface and implementation.

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