Tim Hochberg wrote:
> Guido van Rossum wrote:
>
>> On 4/5/06, Tim Hochberg <[EMAIL PROTECTED]> wrote:
>>
>>
>>> Walter Dörwald wrote:
>>>
>>>
>>>> What's still missing IMHO is a way for an adapter to defer to the next
>>>> adapter in the chain, i.e. something like:
>>>>
>>>>
>> [...]
>>
>>
>>> The concept seems good, but I find the implementation baffling, OK, I
>>> finally figured it out. It only seems to work once though -- you can't
>>> chain super calls. Why not simply raise a DeferToNextAdapter exception?
>>>
>>>
>> I haven't used adapters in years, and I don't recall seeing this in
>> Alex's recent posts; can either of you explain slowly what the use
>> case is and how it's typically used? The code fragments shown so far
>> aren't helping. :-(
>>
>>
> I'm hoping that Walter can give some more realistic examples since I
> don't have real-world experience here. The basic idea is simply to let
> an adapter give up and let the protocol try the next adapter. This could
> happen in a generic function, for instance, if you wanted to try some
> fast algorithm for some specific subtypes, but the algorithm might be
> inappropriate depending on the values of the subtypes. You don't find
> that out till your in the adapter itself.
What I had in mind was something like this for an extensible repr():
xrepr = Protocol("xrepr")
@xrepr.register(list)
def xrepr_list(obj):
return "[%s]" % ", ".join(xrepr(x) for x in obj)
class MyList(list):
...
@xrepr.register(MyList)
def xrepr_MyList(obj):
return "MyList(%s)" % xrepr.super(obj)
Servus,
Walter
> This uses Nick Coghlan's GenericFunction implementation from a few posts
> ago with the DeferToNextAdapter stuff added.
But raising a exception ends the execute of the adapter there. I can't
use the result of the super adapter.
Servus,
Walter
_______________________________________________
Python-3000 mailing list
Python-3000@python.org
http://mail.python.org/mailman/listinfo/python-3000
Unsubscribe:
http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
