[squeak-dev] Re: Instance variable access in superclasses.

Vassili Bykov smalltalkbigot at gmail.com
Wed Nov 26 03:58:40 UTC 2008


On Tue, Nov 25, 2008 at 7:19 PM, Greg A. Woods; Planix, Inc.
<woods at planix.ca> wrote:
> 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.

And thus the fragile superclass problem is born.

The thing is, there are two overlapping but different perspectives
here. From an object-centric view, sure, any state or behavior is
there in the object and where in the hierarchy it comes from is a
minor detail.

However, as far as the code goes, we are talking about distinct chunks
of code, potentially written, maintained and updated by different
people. A subclass depends on the superclass in the same way that code
using a library is a dependent of that library's API. Managing that
dependency has maintainability repercussions, and weakening it is a
good thing.

Cheers,

--Vassili



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