Ruby Classes within Classes (or Modules within Modules)

When the interpreter is going through this file, it is assigning classes like this:

OuterClass = Class.new do 
  def foobar
    puts "FOOBAR"
  end

  InnerClass = Class.new do   
    def barfoo
      puts "BARFOO"
    end
  end
end

So when Ruby encounters the nested class, it assigns it to constant InnerClass which is assigned to constant OuterClass They have no relation to each other whatsoever.

The InnerClass has no inheritance to OuterClass:

  InnerClass.ancestors
  => [InnerClass, Object, Kernel, BasicObject]

When you call OuterClass::InnerClass constant you are refering to the InnerClass constant that is namespaced under the OuterClass contstant which equals the Class.new statement assigned to it.

A good book to read about this is “Metaprogramming Ruby”. It goes into the details of classes, singletons, modules etc.