path_manager.rb

class RoutingSwitch < Trema::Controller
  # ...
  def start_topology
    TopologyController.new { |topo| topo.add_observer @path_manager }.start
  end
end

class PathManager < Trema::Controller
  # ...
  def delete_link(port_a, port_b, _topology)
    @graph.delete_link port_a, port_b
    Path.select { |each| each.link?(port_a, port_b) }.each(&:destroy)
  end