PEP 246 revision

[boisgera at gmail.com]

I had a look at the new reference implementation of PEP 246
(Object Adaptation) and I feel uneasy with one specific point
of this new version. I don't fully understand why it checks
if *the type of* the protocol has a method "__adapt__":

    ...
    # (c) then check if protocol.__adapt__ exists & likes obj
    adapt = getattr(type(protocol), '__adapt__', None)
    ...

As a consequence of this change, you can't define a protocol
as a class that implements __adapt__ anymore.

    class Protocol(object):
        def __adapt__(self, obj):
            ...

Instead, you may inherit from a class "AdaptingProtocol" ...

    class Protocol(AdaptingProtocol):
        @classmethod
        def adapt(cls, obj):
            ...

... that uses a specific metaclass

    class MetaAdaptingProtocol(type):
        def __adapt__(cls, obj):
            return cls.adapt(obj)

    class AdaptingProtocol:
        __metaclass__ = MetaAdaptingProtocol
        @classmethod
        def adapt(cls, obj):
            pass

That seems to be a bit complicated ... A I missing something ?

SB