[Zope3-dev] Re: Usage of IAnnotations disrespects interface declaration

[Christian Theune]

Good Morning,

Philipp von Weitershausen wrote:
> In the issue you write:
> 
>> I can see two ways:
>>
>> 1. Extend the IAnnotations interface to grow the necessary
>>   methods and support the existing use cases
>>
>> 2. Remove the ability from the existing attribute annotation
>>   and re-write the code that uses it to avoid using __iter__
>>   __contains__ and items.
> 
> Both are not acceptable, especially option #1. We can't just change 
> existing contracts as we see fit.

Right. However, I think it's possible to regard this is a bug in the
original contract. Regarding it as a bug might make it possible for us
to change the contract. I agree that we need to be careful about
changing them though.

> Here's what I suggest: We create a new interface based on IAnnotations 
> that expresses __iter__ and __contains__::
> 
>    class IIterableAnnotations(IAnnotations):
> 
>        def __iter__():
>            pass
> 
>        def __contains__():
>            pass

Hmm. Looks like an elegant solution to me. When I wrote those options
down, I thought that extending an interface wouldn't be too bad, but
you're right. Any changes to the API are equally hard to introduce.

However, I guess we should be able to integrate this back into the
IAnnotations. Is there a reason anyone will care about the distincation
of IAnnotations vs. IIterableAnnotations who doesn't know that we hadn't
had those methods originally?

If there is no reason for the distinction, it should go away, at least
long term. I know this comes down to evolving an interface which is
hard/impossible to do anyway.

> Code that needs iteration or containment functionality can adapt to 
> IIterableAnnotations. Adapters that actually provide those methods can 
> register themselves as such (the attribute-annotations adapter will 
> surely be able to do that).

The issue also mentions .items(). Any feelings about that?

Christian

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