Re: Writing an Operating System in Ada

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

On Tue, 19 Jan 2010 10:58:23 -0800 (PST), Shark8 wrote:

>>> But that does remind me, I was thinking it would be good to have
>>> PostScript as the display for the OS, unifying the visual display that
>>> way it would eliminate the need for printer drivers (assuming they're
>>> postscript printers) as well as providing a true WYSIWYG for print-
>>> preview (MS's print preview can be a bit... inaccurate), right?
>>
>> Right, but in an OO system you would barely need PostScript. I doubt
>> anybody would like to program in PostScript, so what is left? Poor as a
>> data carrier, unusable for humans. Doesn't it remind something? XML? (:-))
> 
> So, what's wrong with it being used as a data-carrier?

Nothing, except that there could be better ones and it is uninteresting for
the programmer even to know what is actually used as the carrier.

>>>> There shall be no interfaces at all. Ada 95 had everything needed, i.e.
>>>> abstract types. Introducing interfaces in Ada 2005 was a huge mistake.
>>
>>> Why do you say that?
>>
>> Because there should be a honest MI and no interfaces.
> 
> What do you think of [Delphi-style] properties then? Basically they're
> an specification of some [virtual] field of an object [with indicators
> of it being readable and/or writable] that may either be renaming some
> internal field OR the appropriate getter/setter for a field in the
> implementation. I rather like the idea because it doesn't pollute the
> object-space with so many [publicly visible] getter/setter methods.

This is OK, but unrelated to MI. It about separation of implementation and
specification, which was not accomplished in Ada with respect to fields.
Operations of accessing members should be a primitive. What is visible as a
field should be possible to implement either as a physical field or as
getter/setter operations. MI is independent on this. It is about membership
in more than one disjoint classes. Interface is poor-man's MI, restricted
so some artificially chosen cases, which still do not save from either of
non-existent MI problems.

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