[Zope-dev] improving the utility and adapter lookup APIs

[Martijn Faassen]

Wolfgang Schnerring wrote:
> * On Nov 25, 2009, at 11:17 AM, Thomas Lotze wrote:
>>> What about a simple and consistent API for all components including
>>> utilities, adapters and multiadapters:
>>>
>>> IFoo()
>>> IFoo(x)
>>> IFoo(x, y)
> 
> I quite like the simplicity of this spelling, so I want to be sure
> *why* it must be ruled out. (...or does it, really?)
> 
> I'm thinking that this...
> 
> * Martijn Faassen <faassen at startifact.com> [2009-11-25 22:21]:
>> The last one won't work if we want to maintain backwards compatibility. 
>> The second argument is the default.
> 
> is a valid argument, while this...
> 
> * Tres Seaver <tseaver at palladion.com> [2009-11-25 13:34]:
>> You can't use an arbitrary number of positional arguments for the
>> contexts, because we need to support the named / default cases too.
> 
> is not, as evidenced by...
> 
> * Fabio Tranchitella <kobold at kobold.it> [2009-11-25 20:51]:
>>     IFoo(x, y, default=None, name='something')
> 
> or am I missing something here?

I think the problem would exist if we did something like this:

def IFoo(default, name, *args):
    pass

but if we did something like this we should be okay, I think:

def IFoo(*args, **kw):
    name = kw.get('name', missing)
    default = kw.get('default', missing)
    adapted = args

> So I'm thinking, there is no technical reason that prevents Thomas'
> spelling, and I'm wondering, do we really have to preserve backwards
> compatibility for this case?

I'm not very fond of the second argument interpreted as default. If it 
weren't there I'd be quite interested in the API you're proposing.

But someone needs to think of a feasible upgrade scenario. We could 
instrument all calls to IFoo and see whether a default argument is in 
use, but what then? I'd be hard to distinguish a default argument from 
one we're meant to adapt. I'd also be non-trivial to scan code.

We could perhaps release a special version of 
zope.interface/zope.component that *forbids* the second argument to see 
what bugs pop up, but that'd still not guarantuee we catch all cases.

Regards,

Martijn