Re: Ada 2005 puzzle

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

On Sat, 28 Jul 2012 09:59:27 -0700 (PDT), AdaMagica wrote:

> On Saturday, July 28, 2012 12:37:21 PM UTC+2, Dmitry A. Kazakov wrote:
>>> I see what you mean. But since no objects of abstract types may exist and
>>> somehow you have to provide the private components of derived nonprivate
>>> objects, the proper Ada way (as intended by ARG, I guess) is child
>>> packages.
>>
>> That changes nothing. An abstract type remains abstract. You can derive a
>> non-abstract (and thus necessarily broken) type from it and expose the
>> latter.
> 
> I don't understand what you mean (for non-limited types; I see the problem for limited ones).
> Why is it necessarily broken? It has private and visible parts, so what?

You derive from the type for the sole purpose of being able to write a
function returning an instance of. But the initial reason of being abstract
was to prevent very existence of such functions because the type is
non-functional, abstract.

(The concept of construction per a function is unsound independently on the
limited/non-limited issue with regard to abstract types. An abstract type
may require initialization, but shall have no objects. Even if the
"limited" kludge worked, it would remain broken.)

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