“Interfaces & Abstract Classes unnecessary in Ruby” --> Can someone explain?

Question

I\'m trying to wrap my head around Ruby, and one thing I\'m struggling with is the lack of interface/abstract class support. From googling about, the response I continuously see

Answer 1

there are ways to implement this type of thing, including abstract_type gem. While ruby doesn't require it and has mixins, i think there are cases, like adapters, where you'd want to secure your interface to a set of objects with something more explicit.

also, check out http://metabates.com/2011/02/07/building-interfaces-and-abstract-classes-in-ruby/