passing optional block to a method

bubble_sort.rb

class Array
  def bubble_sort!
    last_unsorted = length - 1
    while last_unsorted > 0
      idx = 0
      while idx < last_unsorted
        if block_given?
          switch = yield(self[idx], self[idx + 1])
        else
          switch = lambda { |a, b| a <=> b }.call(self[idx], self[idx + 1])
        end
        if switch == 1
          self[idx] , self[idx + 1] = self[idx + 1], self[idx]
        end

        idx += 1
      end

      last_unsorted -= 1
    end
    self
  end
end