Ruby craziness: Class vs Object?

Question

I just started playing with JRuby. This is my first ruby post. I had a hard time understanding classes vs objects in Ruby. It doesnt mean like what classes & objects in

Answer 1

In Ruby, everything is an Object including classes and modules. Object is the most low-level class (well, in Ruby 1.9.2 there is also BasicObject but this is an other story).

See the following output.

> Object.ancestors
# => [Object, Kernel, BasicObject] 
> Class.ancestors
# => [Class, Module, Object, Kernel, BasicObject] 
> Module.ancestors
# => [Module, Object, Kernel, BasicObject] 
> String.ancestors
# => [String, Comparable, Object, Kernel, BasicObject]

As you can see, both Class and Module inherits from Object.

Back to your original assertions, you have to understand the difference bewteen

• is_a?
• kind_of'
• instance_of?

They are not interchangeable. is_a? and kind_of? returns true if other is the same class or an ancestor. Conversely, instance_of? returns true only if other is the same class.

> Class.is_a? Object
# => true 
> Class.kind_of? Object
# => true 
> Class.instance_of? Object
# => false