[Python-Dev] PEP 443 - Single-dispatch generic functions (including ABC support) (original) (raw)
Steven D'Aprano steve at pearwood.info
Wed May 29 04:04:57 CEST 2013
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On 29/05/13 07:27, PJ Eby wrote:
On Tue, May 28, 2013 at 3:41 PM, Russell E. Owen <rowen at uw.edu> wrote:
Is it true that this cannot be used for instance and class methods? It dispatches based on the first argument, which is "self" for instance methods, whereas the second argument would almost certainly be the argument one would want to use for conditional dispatch. You can use a staticmethod and then delegate to it, of course. But it probably wouldn't be too difficult to allow specifying which argument to dispatch on, e.g.: @singledispatch.on('someArg') def mymethod(self, someArg, ...): ... [...] So, it's just a few lines added, but of course additional doc, tests, etc. would have to be added as well. (It also might be a good idea for there to be some error checking in wrapper() to raise an approriate TypeError if len(args)<=arg.)
I feel that specifying the dispatch argument in full generality is overkill, and that supporting two use-cases should be sufficient:
dispatch on the first argument of functions;
dispatch on the second argument of methods, skipping self/cls.
After all, is this not supposed to be simple generics? :-)
I'm vaguely leaning towards @singledispatch and @singledispatch.method for the colour of this bike shed.
-- Steven
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