# Return an array of all values sorted with their keys using `comparator`.
	#
	# ~~~
	# var map = new HashMap[Int, String]
	# map[10] = "ten"
	# map[2]  = "two"
	# map[1]  = "one"
	# assert map.values_sorted_by_key(default_comparator) == ["one", "two", "ten"]
	# assert map.values_sorted_by_key(alpha_comparator) == ["one", "ten", "two"]
	# ~~~
	fun values_sorted_by_key(comparator: Comparator): Array[V]
	do
		var keys = self.keys.to_a
		comparator.sort(keys)
		return [for k in keys do self[k]]
	end