custom_flatten.md

class FlatArray
  attr_reader :nested_array, :flatten_array

  def initialize(nested_array = [])
    @nested_array = nested_array
    @flatten_array = []
  end

  def call
    flat(nested_array)
    flatten_array
  end

  private

  def flat(nested_array)
    nested_array.each do |element|
      if element.is_a? Array
        flat(element)
      else
        @flatten_array << element
      end
    end
  end
end