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

[Devin Jeanpierre]

On Thu, May 23, 2013 at 2:04 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Thu, 23 May 2013 12:12:26 +1000
> Nick Coghlan <ncoghlan at gmail.com> wrote:
>> The binary operators can be more accurately said to use a complicated
>> single-dispatch dance rather than supporting native dual-dispatch.
>
> Not one based on the type of a single argument, though.

Why not?

I'd expect it to look something like this:

    @singledispatch
    def ladd(left, right):
        return NotImplemented

    @singledispatch
    def radd(right, left):
        return NotImplemented

    def add(left, right):
        x = ladd(left, right)
        if x is not NotImplemented:
            return x
        x = radd(right, left)
        if x is not NotImplemented:
            return x
        raise TypeError

Then instead of defining __add__ you define an overloaded
implementation of ladd, and instead of defining __radd__ you define an
overloaded implementation of radd.

-- Devin