[Twisted-Python] adapt from more than one interface
esteve at sindominio.net
Sun Apr 12 11:11:12 EDT 2009
On Sunday 12 April 2009 15:16:04 glyph at divmod.com wrote:
> Sorry for that; it certainly wasn't my intention. I meant just what I
> said: I find it difficult to communicate about. Perhaps I should have
> said, "trust me, my experience suggests that it is".
I'm too thin-skinned sometimes, so just forget what I said :-)
> And this is why the explanation of its wrong-ness is difficult. I know
> that you could get the same effect by doing (IFoo, IUsernamePassword) ->
> IBar and (IFoo, IHostnamePath).
Actually I just discovered some of those flaws in Zope's adapter registry, so
you're right that multi-adapters are not that easy to implement.
> Would the specifics of your application allow you to introduce an
> intermediary IProtocolFactoryConfigurer interface, with .config* methods
> that would return the actual ProtocolFactory, as with my IBarFactory
> above? "IBar" here would be IProtocolFactory; sorry for the confusion
> with the word "factory".
I guess that would be sufficient, an "adapter factory" in some sense. In fact,
I already came up with something similar, but found it too cumbersome
(attached). Maybe, instead of supporting multi-adapters, a recipe like yours
could be added to the documentation.
> So ConfigurationObject is purely for the IFooFactory implementation?
Yep. In our case, AMQP protocol instances require some arguments to be passed
(e.g. username and password for connecting to the broker). BTW, I just
realized that we should use usage.Options instead of our own config object.
> Thanks for that link, by the way, that's a great introduction to
> zope.component. Not one I'd seen before.
It covers pretty much everything about adapters and interfaces, I found it
very detailed and useful.
> I'm still not a big fan of multi-adapters, but the code's so short, and
> so non-invasive (in particular I don't believe it'll affect the
> performance of "normal", single adaptation), that I probably wouldn't
> argue too hard against it. Feel free to file that ticket, although I
> won't promise that somebody *else* won't come along and object. In any
> case, you can start using it right away if it suits you :).
It's very simple and elegant, I like it :-) I think it's a good idea to
include it, or maybe add an entry to the FAQ.
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