In addition to the other answers, Class defines the method === to test whether an object is an instance of that class.
- o.class class of o.
- o.instance_of? c determines whether o.class == c
- o.is_a? c Is o an instance of c or any of it's subclasses?
- o.kind_of? c synonym for *is_a?*
- c === o for a class or module, determine if *o.is_a? c* (String === "s" returns true)