In this section, we are going to walk through how to build a nested iterator with a practical example, namely looping over a nested hash in Ruby.
Before we move on, I'd like to warn you that you have to be careful while working with nested iterators because they can cause performance issues if poorly implemented. If you are working on a collection within another collection, you will go through all the elements in the nested collection when an element of the parent collection is called. This means you will go through a large number of iterations that can potentially slow your program down by quite a bit. Sometimes, the program may even crash if you have to iterate through thousands of elements across multiple collections. So be careful while using these nested iterators.
