[Python-Dev] PEP 443 - Single-dispatch generic functions

[Guido van Rossum]

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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-- 
--Guido van Rossum (python.org/~guido)