Hash.new « Hash « Ruby

1.Creating Hashes
2.You can test to see if a hash is empty with empty?
3.Test how big it is with length or size
4.use new to create a hash with a default value which is otherwise just nil
5.access any key in a hash that has a default value
6.Hash with =>
7.Hash.new with block logic
8.This lazily initialized hash maps integers to their factorials