Perhaps a silly question. What is the best way to add a randomize
method to array? I know that this code will properly randomize an
array:

a.sort_by{ rand }

but I wonder how I can know add this to the array class. I can't
assign self to the result of this method, so this will not work:

class Array
  def randomize
    self = self.sort_by{ rand }
  end
end

What is the best way to do this?