Question

If I have a class like this:

class Component (val name, val description, var subElements : Set[Component])

How can I test if a Component contains cycles inside (with a Boolean function) and who started this cycle.
I know well that if I use val instead of var avoid cycles, but I cannot use val.

Answer 1

A member of Component to return all elements in the graph below which start a cycle. It returns an empty set if there are no cycles.

def descendantsWithCycle = {
  def findCycle(current: Component, checked: Set[Component]): Set[Component] =
    if (checked contains current) Set(current)
    else {
      val newChecked = checked + current
      current.subElements.flatMap(findCycle(_, newChecked))
    }

  findCycle(this, Set())
}