[Python-Dev] PEP 443 - Single-dispatch generic functions (original) (raw)

Guido van Rossum guido at python.org
Thu May 23 05:26:56 CEST 2013

Funny. I thought that the PEP was quite strong enough already in its desire to stay away from multi-dispatch. But sure, I don't mind making it stronger. :-)

On Wed, May 22, 2013 at 7:12 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

On Thu, May 23, 2013 at 10:14 AM, Glenn Linderman <v+python at g.nevcal.com> wrote:

Yet about half of the operator overloads would be incomplete if there were not corresponding r* methods (radd, rsub, etc.) because the second parameter is as key to the dispatch as the first.

While unary operators, and one argument functions would be fully covered by single dispatch, it is clear that single dispatch doesn't cover a large collection of useful cases for operator overloading. The binary operators can be more accurately said to use a complicated single-dispatch dance rather than supporting native dual-dispatch. As you say, the PEP would be strengthened by pointing this out as an argument in favour of staying away from a multi-dispatch system (because it isn't obvious how to build a comprehensible one that would even support our existing NotImplemented based dual dispatch system for the binary operators). Cheers, Nick. -- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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