# Returns the weak connected components of this digraph.
	#
	# The weak connected components of a digraph are the usual
	# connected components of its associated undirected graph,
	# i.e. the graph obtained by replacing each arc by an edge.
	#
	# ~~~
	# var g = new HashDigraph[Int]
	# g.add_arc(1, 2)
	# g.add_arc(2, 3)
	# g.add_arc(4, 5)
	# assert g.weakly_connected_components.number_of_subsets == 2
	# ~~~
	fun weakly_connected_components: DisjointSet[V]
	do
		var components = new DisjointSet[V]
		components.add_all(vertices)
		for arc in arcs_iterator do
			components.union(arc[0], arc[1])
		end
		return components
	end