I don't think I'd call len pure for OOP. Rather, having a top-level definition--len(array) instead of array.length--gives us functional purity. That is, it disc

I don't think I'd call len pure for OOP. Rather, having a top-level definition--len(array) instead of array.length--gives us functional purity. That is, it discards (or hides) the concept of message passing and treats top-level methods like mathematical functions. Lately I've heard a lot of chatter about Ruby Interfaces. They could be useful to achieve better unity. Though the Ruby collection API is already pretty consistent.