[Python-3000] PEP 3133: Introducing Roles (original) (raw)

Collin Winter collinw at gmail.com
Wed May 16 00:30:13 CEST 2007

On 5/14/07, Steven Bethard <steven.bethard at gmail.com> wrote:

On 5/14/07, Collin Winter <collinw at gmail.com> wrote: > There really is no difference between roles and all- at abstractmethod > ABCs. From my point of view, though, roles win because they don't > require any changes to the interpreter; they're a much simpler way of > expressing the same concept.

Ok, you clearly have an implementation in mind, but I don't know what it is. As far as I can tell: * metaclass=Role ~ metaclass=ABCMeta, except that all methods must be abstract * performrole(role)(cls) ~ role.register(cls) * performs(obj, role) ~ isinstance(obj, role) And so, as far as I can see, without an Implementation section, all you're propsing is a different syntax for the same functionality. Was there a discussion of your implementation that I missed? > You may like adding the extra complexity > and indirection to the VM necessary to support > issubclass()/isinstance() overriding, but I don't. Have you looked at Guido's issubclass()/isinstance() patch (http://bugs.python.org/1708353)? I'd hardly say that 34 lines of C code is substantial "extra complexity".

This is what I don't understand: ABCs require changing the VM, roles don't; all that change buys you is the ability to spell "performs()" as "isinstance()". Why are ABCs preferable, again?

Collin Winter

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