# To use this, simply require this file and it will become an extension of the base Array class. As such you can then do
# [1,2,[3]].custom_flatten as in Array.flatten instance method.
class Array
  def custom_flatten(array=self)
    array.each_with_object([]) do |e, flattened|
      flattened.push *(e.is_a?(Array) ? custom_flatten(e) : e)
    end
  end
end