Oren Tirosh wrote: > On Wed, Aug 14, 2002 at 10:08:59AM -0400, Andrew Koenig wrote: [snip] > > Why? That is, why can't you imagine making a claim that type > > X meets interface Y, even though the author of neither X nor Y > > made that claim? > > It's not a failure of imagination, it's a failure of terminology. In > contexts where the term 'interface' is used (Java, COM, etc) it usually > means something you explicitly expose from your objects. I find that the > term 'category' implies something you observe after the fact without > modifying the object - "these objects both have property so-and-so, let's > group them together and call it a category". Okay, but in Python interfaces as we know them (the Scarecrow descended interfaces as in use in Zope 2 and Zope 3), you can say things like this (with some current limitations concerning basic types). Usually however one does use the __implements__ class attribute, but that's because it's often clearer and easier when one is writing a new class. [snip] > That's why the intelligence should be in the membership predicate, not in > the classes it selects. Nothing needs to be changed about types. > Conceptually, categories apply to *references*, not to *objects*. They help > you ensure that during execution certain references may only point to > objects from a limited category of types so that the operations you perform > on them are meaningful (though not necessarily correct). This is quite different from the Zope interfaces approach, I think. Zope interfaces do talk about objects, not references. This is leaning towards a more static feel of typing (even though it may be quite different from static typing in the details), which I think should be clearly marked as quite independent from a discussion on interfaces. Though I'd still call your beasties Interfaces and not categories, even though you want to use them in a statically typed way -- but please let's not reject simple interfaces just because we may want to do something complicated and involved with static typing later.. Regards, Martijn
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