At 04:59 PM 5/10/2006 +0200, Marcin 'Qrczak' Kowalczyk <[EMAIL PROTECTED]> wrote: >Explicitly declared interfaces have a partial order, which is useful >for dispatch.
Note that if the notion of "interface" is reduced to "a set of generic functions to which an object may be passed", then it's not necessary to have explicit interface declaration - it's an automatic side effect of implementing methods for the generic functions involved. It also avoids reifying interfaces as concrete objects, except as a convenient way to refer to groups of generic functions. Implementing this approach is actually a straightforward extension of Guido's overloaded function implementation, by replacing issubclass() with a generic function "implies()". When comparing two classes, "implies()" would do the same as issubclass() (modulo the appropriate argument order), but it would also need to support comparing interface assertions with each other and with classes. Overloaded functions would also need a "supports()" method to indicate whether the function has an unambiguous implementation for a given input signature. These are very straightforward extensions -- a mild refactoring at most. The only complicating factor in a production implementation would be that adding new methods at runtime to something like iter() would need to invalidate the signature caches of any generic functions with registered signatures based on iterability. That means some kind of notification facility. It'd be nice if it also worked for changes to a class' __bases__. >There is little hope for inferring inclusions among >arbitrary predicates. It's true that inferring inclusions among truly arbitrary predicates is impractical, but it *can* readily be done for any N kinds of predicates, where N is however many you choose to implement. RuleDispatch in fact uses a generic function to transform predicates into objects that can be ordered by inclusion, which allows applications with special needs to register new transformations. (The built-in transformations change 'isinstance()' and 'issubclass()' subexpressions into class-based criterion objects, for example.) However, I'm not advocating that this kind of capability to be added to Python directly; I'd just like to be able to integrate RuleDispatch's more advanced features into whatever overloading machinery Python ends up with. _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
