Mastering data structures in Ruby 

To close up this series, I want to introduce the concept of persistent data structures, a term coined by Driscoll et al. in an article from 1986 that these days it’s at the core of most purely functional data structures.The first time I heard the term was in a talk by Rich Hickey, the creator of Clojure, where he showed how Closure’s data structures internally deal with mutations (or the lack of them, actually).On this post, we are going to implement a “persistent” linked list, which is a data structure that behaves almost the same as the singly linked lists that we built in the first post of this series but is immutable and has a copy on write semantics.