[Python-3000] Fw: typeclasses, duck-typing

[Ben.Young at risk.sungard.com]

"Phillip J. Eby" <pje at telecommunity.com> wrote on 11/05/2006 16:09:47:

> At 10:12 AM 5/11/2006 +0100, Ben.Young at risk.sungard.com wrote:
> >A dynamic version of concepts (I guess a combo of multi-methods and
> >adaptation) would be great for Python, but it's hard to see how it 
could
> >be done simply and efficiently.
> 
> Go back and read the post where I explained how, then.  ;)
> 
> Seriously, it can be done as a pretty straightforward refactoring of 
> Guido's existing overloaded function implementation.  You just need to 
be 
> able to pass in objects other than classes to define a signature.
> 
> But I suppose maybe it's one of those things that's only obvious and 
> straightforward to me, so I'll have to see if I can carve out some time 
> this weekend to implement a demo.
> 
> The harder problem is having a way to define overloaded methods that's 
at 
> least as convenient as 'def __iter__(self):' -- but that's a syntax 
issue.
> 
> It seems to me, however, that having something like a 'defop' keyword 
would 
> do the trick, if you also had argument types.  So if you were 
implementing 
> UserList or UserDict, you could have some code like this in the class 
body:
> 
>      defop len(self):
>          return len(self.data)
> 
>      defop iter(self):
>          return iter(self.data)
> 
>      defop operator.getitem(self, key):
>          return self.data[key]
> 

Why not

class Foo(object):
        @specialize(arg(0))
        def core.len(self)
                ...


I think this is somewhat how PyPy specializes some of its methods (modulo 
syntax)

I don't know how this would appear in the class dict though? self.len()?

Cheers,
Ben