[Python-Dev] single dispatch for instance methods (original) (raw)

Tim Mitchell tim.mitchell at leapfrog3d.com
Sun Oct 16 20:55:17 EDT 2016

An interesting idea, however from my point of view in methoddispatch there is no dispatching on the self argument at all. Overriding methods simply allows your subclass to have a different dispatch table for a method than the super class. This happens when the class is created, not when the function is called. When the method is called it is single-dispatched on the (single) argument after self using the dispatch table for the class of the method.

On 17 October 2016 at 11:53, Aric Coady <aric.coady at gmail.com> wrote:

On Oct 14, 2016, at 8:49 AM, python-dev-request at python.org wrote:

Date: Fri, 14 Oct 2016 14:11:18 +1300 From: Tim Mitchell <tim.mitchell at leapfrog3d.com> It would be nice if the @singledispatch decorator worked on instance methods. I have a reference implementation on pypi that does this ( https://pypi.python.org/pypi/methoddispatch).

You might be interested in this thread from my multimethod library: https://bitbucket.org/coady/multimethod/issues/2/. It was a feature request for multiple dispatch to work on instance methods. I implemented a variation where the initial self argument still contributed to the dispatch. I think the same reasoning would apply in the single dispatch case: that it’s not obvious the “dispatch” would occur once on the self argument to find the method, and then again on the “first” argument. Especially since Py3 did away with bound methods, so you can call a method through its class and explicitly supply self as the first argument.

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