This is a simple implementation of a hash map in Ruby that I did as an exercise just for fun. It could feasibly replace Ruby's built-in Hash class, but really that would be sort of pointless.

A HashMap can be initialized simply using HashMap.new, and you can optionally give it an array of subarrays containing a key and value in order to instantiate it with those keys and values. From there, a number of methods based on Ruby's built-in Hash class are available, such as get/[], insert/[]= and include?/has_key? It includes the Enumerable module, so favorite methods such as each and map work like a charm.

The HashMap is initialized with a number of buckets, which take the form of doubly linked lists whose links store a key and value. When a new item is inserted into the HashMap, a hashing operation is performed on that item's key, the result of which is modulo'd to find which bucket the item belongs in. The item is then inserted at the end of the LinkedList represented by the bucket. If the number of items exceeds the number of buckets, the number of buckets is automatically doubled in order to keep the runtime complexity to a minimum.