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Date: Mon, 26 Dec 2011 00:37:22 +1100
Subject: Re: Adding an interface to existing classes
From: Chris Angelico <rosuav@gmail.com>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:17894

On Mon, Dec 26, 2011 at 12:27 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> There's nothing in the above that assumes that other has the same type as
> self. It's just that the type of other is ignored, and the type of self
> always wins. I find that a nice, clear rule: x.intersection(y) always
> returns a point with the same type as x.

The intersection of DrawableLine and DrawableLine is DrawablePoint.
That's not the same type as either of the inputs. Same if you seek the
intersection of two planes, which is a line - or two spheres, which is
a circle (with possible failure if they don't intersect).

ChrisA