Musing on the Ruby object model in Ruby 1.8.7 vs. 1.9.3

eigenclasses.rb

obj = Object.new
puts "obj is #{obj}"

eigobj = class << obj
  self
end
puts "Eigenclass of obj is #{eigobj}"
puts "Superclass of the eigenclass of obj is #{eigobj.superclass}"

eigclassobj = class << obj.class
  self
end
puts "Eigenclass of the class of obj is #{eigclassobj}"

if eigclassobj == eigobj.superclass
  # this is true for Ruby 1.8.7
  puts "Eigenclass of the class of an object is the same as the Superclass of the Eigenclass of an object" 
  
  def eigclassobj.hello
    puts "This is a method defined on the Eigenclass of the class of obj, but called on the Superclass the Eigenclass of obj"
  end
  eigobj.superclass.hello

else
  # this is true for Ruby 1.9.3
  eigeigobjsuper = class << eigobj
    self.superclass
  end
  puts "Superclass of the eigenclass of the eigenclass obj is #{eigeigobjsuper}"
  
  if eigclassobj == eigeigobjsuper
    puts "Eigenclass of the class of an object is the same as the Superclass of the Eigenclass of the Eigenclass obj"
    
    def eigclassobj.hello_again
      puts "This is a method defined on the Eigenclass of the class of obj, but called on the Superclass of the Eigenclass of the Eigenclass of obj"
    end
    eigeigobjsuper.hello_again
  end
end

output.txt

# Ruby 1.8.7
obj is #<Object:0x10505b148>
Eigenclass of obj is #<Class:#<Object:0x10505b148>>
Superclass of the eigenclass of obj is #<Class:Object>
Eigenclass of the class of obj is #<Class:Object>
Eigenclass of the class of an object is the same as the Superclass of the Eigenclass of an object
This is a method defined on the Eigenclass of the class of the object, but called on the Superclass the Eigenclass of the object

# Ruby 1.9.3
obj is #<Object:0x007ff60a1dffa8>
Eigenclass of obj is #<Class:#<Object:0x007ff60a1dffa8>>
Superclass of the eigenclass of obj is Object
Eigenclass of the class of obj is #<Class:Object>
Superclass of the eigenclass of the eigenclass obj is #<Class:Object>
Eigenclass of the class of an object is the same as the Superclass of the Eigenclass of the Eigenclass obj
This is a method defined on the Eigenclass of the class of the object, but called on the Superclass of the Eigenclass of the Eigenclass of the object