defmodule Plane do
  defstruct is_fueled?: false, has_pilot?: false

  def take_off(plane) do
    case plane do
      %Plane{ is_fueled?: false } ->
        :needs_fuel
      %Plane{ has_pilot?: false } ->
        :needs_pilot
      _ ->
        :whoosh!
    end
  end
end

plane = %Plane{is_fueled?: true}
Plane.take_off(plane)
# => :needs_pilot

plane = %Plane{has_pilot?: true}
Plane.take_off(plane)
# => :needs_fuel

plane = %Plane{has_pilot?: true, is_fueled?: true}
Plane.take_off(plane)
# => :whoosh!