Last login: Tue Sep  2 21:05:10 on ttys000
~ $ irb
irb(main):001:0> module Foo
irb(main):002:1> def self.bar
irb(main):003:2> puts 'here in bar'
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> class Bar
irb(main):007:1> include Foo
irb(main):008:1> end
=> Bar
irb(main):009:0> Bar.bar
NoMethodError: undefined method `bar' for Bar:Class
	from (irb):9
	from :0
irb(main):010:0> class Bar
irb(main):011:1> extend Foo
irb(main):012:1> end
=> Bar
irb(main):013:0> Bar.bar
NoMethodError: undefined method `bar' for Bar:Class
	from (irb):13
	from :0
irb(main):014:0>