Failure of `extend self`

gistfile1.txt

require 'ostruct'

module Normalizer
  extend self
  def trim(str)
    str.strip
  end
end

obj = OpenStruct.new
obj.extend Normalizer
obj.trim = 'You must trim 5 spaces!'
obj.trim # fails, because it's hitting Normalizer#trim, wouldn't happen with module_function

BOOM! It does work, you are attempting to mix this the wrong way.

>> module Normalizer
>>     extend self
>>     def trim(str)
>>         str.strip
>>       end
>>   end
=> nil

>> module TestModule
>>   def trim(str)
>>     "NOPE!"
>>     end
>>   end
=> nil
>> Normalizer.extend TestModule
=> Normalizer
>> Normalizer.trim("ok")
=> "NOPE!"