[gregwebs]

Generally speaking I like interfaces, but Ruby is so dynamic that you couldn't use them for compile-time guarantees. Interfaces could only get you a slightly nicer way of dynamic duck typing. I wouldn't really call all of the dynamism a strength though - one of the limiting factors of compile time evaluation here is that a method can later become undefined- when is the last time you needed that?

[steveklabnik]

Actually, undefining methods on an object because such an idiom that Ruby 1.9 introduced a new base class into the hierarchy: BasicObject. [1] This is now the new root class, above Object.

1: http://www.ruby-doc.org/core-1.9/classes/BasicObject.html

[gregwebs]

Yeah, that is the 1 case, and ActiveSupport has had a BasicObject for a while now. This is another case where proponents would say it is great that you can undefine a method, but I would say that is a hack for lack of any namespace management. Now that there is a BasicObject I am not sure that there is any practical use for undefining a method- probably only for dealing with namespace collisions, which again seems to point out a language flaw, not a feature of dynamism.