[Zope-dev] split out zope.component "mechanics" into a separate package (was Re: improving the utility and adapter lookup APIs)
faassen at startifact.com
Sat Nov 28 06:25:12 EST 2009
Chris McDonough wrote:
> It tries to address the following problem.
> Currently people seem to get wrapped around the axle and confused by the
> purpose of "the ZCA", which currently implies at least two different things:
> - Machinery to perform complex registrations and lookups using interfaces
> in the form of a registry.
> - A global API that presents a view of the world: "there are these things
> called utilities and adapters, and this API is how you do adaptation and
> utility lookup".
> These two things are conceptually distinct.
> It shouldn't be necessary to need to understand the concept of "utility" and
> "adapter" to use a registry. A registry is just machinery that uses interfaces
> as registration markers for the benefit of later arbitrary lookups, not
> necessarily just for "finding utilities" or "finding and calling adapter
> factories". For instance, you might use the registry to register some callable
> that accepts *no* arguments with, say, two "requires" arguments. You shouldn't
> need to call this an "adapter", because it's not one; you just want to register
> something and get it back when you ask nicely.
Agreed, but isn't this registry in zope.interface already? I mean
zope.interface.adapter.AdapterRegistry? I've used this for the
"not-really-adapting-as-I-don't-want-to-call" in a library of mine
You factored out the registry functionality, but there are still plenty
of references to utilities in it, for instance. As far as I understand
it that would be putting too much into zope.registry already?
> The API of a registry should be able to evolve separately from the API of its
> consumers (the global ZCA API is only one consumer). The current registry API
> permits the concepts of utility and adapter to bleed into the implementation,
> but this needn't be the case forever. We could provide (and document) a very
> simple registry base class with a normalized API that didn't have any of this
> conceptual baggage; it would be extremely popular, I think.
> Likewise, it should be possible to use a different registry implementation to
> service the ZCA global API. This is possible right now via
> getSiteManager.sethook, of course.
>> You factored various related things together - perhaps it would make
>> sense to do this refactoring within zope.component?
>> I'm +1 on making zope.event part of zope.component and deprecating
>> Speculating, would it instead make sense to move zope.registry
>> functionality into zope.interface? The only additional dependency is
>> zope.event. At first glance the answer would be "no" as it really
>> introduces various component architecture concepts...
> It might make sense to me to put a very simple component registry in
> zope.interface: it already has the concept of "adapter" baked in.
Yeah, I think this makes more sense.
So, we have a number of projects:
* interface API - the stuff around calling interface I sketched out
elsewhere. I think this is relatively low-hanging fruit. On the other
hand it breaks backwards compatibility. I wouldn't want this project to
depend on the other improvements, and I don't think it has to, so I'd
like to see this as zope.component 4.0.
* improving and move code that's general enough from zope.component into
zope.interface. What this would look like I'm not quite sure about yet,
as zope.registry at first glance contains a lot of knowledge about
utilities and such still. There are backwards compatibility issues
surrounding persistence but hopefully less around the APIs themselves.
* an improved registration API for zope.component. This would affect a
lot of code that does registration.
Documentation projects should go along with all of those.
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