2008/11/26 Greg A. Woods; Planix, Inc. <woods at planix.ca>:
>
> On 25-Nov-2008, at 7:57 PM, Igor Stasenko wrote:
>>
>> I like the idea of hiding the state/storage specific details from eyes
>> of subclasses.
>> It makes irrelevant, in what format or where particular object holds its
>> state.
>> As long as you providing messages to access it, it could be anything.
>
> So why not just get rid of instance variables completely?   :-)
>
> I think Ramon Leon hit the nail on the head.   You're not supposed to try to
> protect anything in a class definition from any of its subclasses.
>  Inheritance is a mechanism to _expand_ upon the definition of a class, not
> restrict it.
>
> An instance of an object contains all of the components (instance variables,
> methods, etc.) of the class it belongs to as well as, by definition, all of
> the components from any (and all) class(es) it inherits from.  That's the
> whole idea, as I understand it, underlying the concept of inheritance.
>
> An object shouldn't have to use accessor methods to get at its own internal
> state, no matter where in the class hierarchy its state may be defined.
>  "super" is only needed to get around explicit re-definitions done by the
> subclass.

My understanding of inheritance is different, in short:
A subclass of particular class is a _specialization_ of base class,
not  _expansion_.

An instance of subclass provides same interface as base class, but
with possibly different behavior (because of overrides) or provide
additional specialized interface (by introducing new methods).

If you look from a user's point of view (outside a class), you could
only send a messages to it. So, for you, as for user its not relevant
where an object holds its state - you only interested in its
behavior/interface.

As for subclass - a subclass interested in inheriting same interface
as base class. Inheriting a state information having a little
importance, its just an implementation detail for outside user of
class, because anyways he unable to operate with this state directly.

>
> --
>                                        Greg A. Woods; Planix, Inc.
>                                        <woods at planix.ca>
>


-- 
Best regards,
Igor Stasenko AKA sig.