Immutable data does not necessitate copying the entire structure when it is shared or changed. I encourage you to take a look at persistent data structures[0].

Immutable data does not necessitate copying the entire structure when it is shared or changed. I encourage you to take a look at persistent data structures[0]. Okasaki's "Purely Functional Data Structures"[1] is a good resource if you'd like to look at this in more depth. Rich Hickey's talk about the implementation of persistent data structures in Clojure is also a nice introduction[2]. [0]: https://en.wikipedia.org/wiki/Persistent_data_structure https://en.wikipedia.org/wiki/Persistent_data_structure [1]: http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf [2]: https://www.infoq.com/presentations/Value-Identity-State-Rich-Hickey https://www.infoq.com/presentations/Value-Identity-State-Ric...