00205.rb

class Module
  def ===(object)
    object.kind_of?(self)
  end
end

class Foo < BasicObject
  def x
    3
  end
end

Foo.new.instance_eval do
  Kernel.puts x
end

# On MRI:
#
#      3
#
# On Rubinius:
#
# An exception occurred running /home/arne/projects/ruby-tmp/00205.rb:
#
#     Unable to send 'kind_of?' on instance of BasicObject (NoMethodError)
#
# Backtrace:
#
#   BasicObject(Foo)#kind_of? (method_missing) at kernel/common/basic_object.rb:3
#                                   Module#=== at /home/arne/projects/ruby-tmp/00205.rb:3
#               BasicObject(Foo)#instance_eval at kernel/common/eval.rb:24
#                            Object#__script__ at /home/arne/projects/ruby-tmp/00205.rb:13
#             Rubinius::CodeLoader#load_script at kernel/delta/code_loader.rb:66
#             Rubinius::CodeLoader.load_script at kernel/delta/code_loader.rb:152
#                      Rubinius::Loader#script at kernel/loader.rb:649
#                        Rubinius::Loader#main at kernel/loader.rb:825