On Thu, 2004-01-08 at 16:24, Jonathan Lang wrote: > In this example, there's no difference between the Dog and Tree roles; > however, this would almost certainly not be the case most of the time - at > the very least, a class with a Dog role would have @.legs, while a class > with the Tree role would have @.branches. However, if all that happens > when you specify a demand for the Dog role in a signature is that the > object must meet Dog's demands, then both crossPerson and Trog will be > accepted.
I would consider that a mistake. All that doing a role should imply is that somehow, that class understands the syntax *and* semantics of the methods of that role. Introspection can't reliably reveal whether $some_object.bark accesses a property (noun) or a method (verb). It's true that looking for @.legs versus @.branches could get you closer, but I'm not sure that it's been decided whether methods of a role should blissfully ignore all of the object's state. Besides, in a delegation situation, there could easily be some sort of magic that handles those attributes that the introspection mechanism might miss. -- c
