Inheritance and name clashes

[Steve Howell]

On Oct 3, 5:13 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
> On Oct 3, 3:04 pm, Rock <rocco.ro... at gmail.com> wrote:
>
> > No, I was just working with a normal library
> > class which was supposed to be derived. So that's what I did, but in
> > the process I found myself needing to create an instance variable and
> > it dawned on me: "how do I know I'm not clobbering something
> > here???" ... I'd have to look at the docs, right? But I still wasn't
> > sure ... so, then I thought "let's look at the source", and then I
> > found out. But! It took me some time to make sure, and I was puzzled
> > as well. I mean, what if I have no source to look at? What if the
> > library I'm using doesn't realase the source, or what if I just can't
> > get my hands on it for some reason or another?
>
> > That was a big disappointment with Python for sure. Somehow PHP makes
> > me feel a little safer, in that respect at least.
>
> Name collisions are only one of several pitfalls that can happen when
> you subclass a third-party clasa.  Another pitfall is uncertainly over
> which methods a certain behavior is implemented, which is something
> you can't determine from the interface alone, in any language I'm
> aware of.  If you want to override such a behavior you have to look at
> the class's implementation to find out how.  Point is, if Python
> corrected this "defect", you still wouldn't be "safe" because there
> are other dangers, which exist in other langauges, too.
>
> Now, if a class is specifically designed to be subclassed by third-
> party users, and it's not using name mangling or some other way to
> avoid name collisions, then I would call it defective.
>

Yep, and a well-designed library can go a long way toward avoiding
name collisions simply by providing an API that facilitates logical
extensions.  If a library knows when it needs to delegate to a caller,
it can have a callback mechanism.  If a library knows how subclasses
are likely to change its state, it can provide an API that lowers the
temptation to muck with internals.