[Baypiggies] Possible talk: A Nondualist Alternative to Proxy Wrapper Theory
ken at seehart.com
Sat Jun 23 14:25:52 CEST 2007
If you read my previous email that was accidentally sent here instead of
python.org, you have some idea of what this is about.
What is new is that I did some experimenting and came up with some
interesting results. In fact I have implemented a proof-of-concept of
what I describe below.
So let me know if you would like me to give a talk on this subject.
Anyone who has wrapped C or C++ libraries that contain methods which use
and/or return instances of the types that are being wrapped has
encountered what I call the /inheritance/proxy wrapper dilemma/.
The general scenario is that we have a python extension library which we
wish to enhance by writing a python layer to add functionality and
improve syntax. A good example is the wxPython library. The most
obvious thing to do is to derive our classes from the extension types.
This works fine until we have to deal with methods in the extension
library that create and return instances of the low level types. We
want to only expose instances of our classes, not the low level objects.
At this point we do a little research and find out that we should be
using composition rather than inheritance. So we make a proxy system
and inevitably wind up with a rather unwieldy pile of meaningless
wrappers on all of our methods. This solution is generally considered
better than inheritance, but it creates a new set of problems. Two
obvious problems associated with the proxy solution are the extra
function call overhead of the wrappers, and the necessity of generating
piles of boilerplate code. Also there is a tendency for the dualism
between the proxy object and the raw object to be an ongoing annoyance.
Once most of the bugs are weeded out, the proxy system works adequately,
but can't really be considered fun.
A Nondualist Alternative to Proxy Wrapper Theory:
In this talk, I will demonstrate a technique for implementing wrappers
without proxies that nevertheless have all the desirable features that
we expect from composition based solutions, and all the simplicity we
had hoped for with simple inheritance. We eliminate dualism along with
the unnecessary run-time overhead of wrappers. The challenge is to keep
an open mind when faced with scary seeming violations of well
established object oriented theory, and focus on the practical
Time: 45 minutes to 1 hour. Probably not for beginner night :-) Let me
know if you are interested.
- Ken Seehart
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