TIL, Immutable doesn’t mean slow

In elixir, to add an item to list, we write like this

list1 = [1, 2, 3]
list2 = [0 | list1]

If it was me, I have 2 options to implement: clone list1 or point list1 to list1. Seems, cloning list1 is prefered, after lots of pain with data changed in ruby 😂 But if creating list2 clones list1, it’ll be slow. Memory consumed, time for GC… Chosing pointing, what if list1 changed?

Wait!

elixir is immutable, that means, list1 isn’t changed, that means, we needn’t care about breaking list2 in this way.

Another point is, elixir list is linked list. So, it’s native faster to implement the pointing way.

Extract from Programming Elixir 1.6, Chapter 3