Flatten the array in ruby without using inbuilt Array#flatten

flatten-array.rb

#!/usr/bin/env ruby

def flatten(array)
  array.each_with_object([]) do |e, flat|
    flat.push *(e.is_a?(Array) ? flatten(e) : e)
  end
end

print flatten([[1, 2, 3, 4], 5, 6, [[7, 8], 9, 0]])