Iterate through a list that has another list that has another list etc

Question

So I have a list of a specific class I have defined let's say IList<Element> A; the Element class has IList<Children> b;

B list gets it's data from a file. B could have a list that contain a list that contain list etc... "Recursively" or B could have only a single list i.e B the nested lists could vary

I want to iterate on all the lists. is there a possible way to do it?

Answer 1

The naive approach is simply stack recursion - it is fine for many common scenarios:

class A {
    List<B> _theList;
    void DoTheThing() {
       foreach(var b in _theList) b.DoTheThing();
    }
}
class B {
    List<B> _innerItems;
    void DoTheThing() {
        DoTheThingAtThisLevel();
        // and now recurse
        foreach(var inner in _innerItems) inner.DoTheThing();
    }
}

This can be a problem for very deep lists - as the stack can get too big; in that case, using a local queue or stack and using that for the logical state can avoid that:

class A {
    List<B> _theList;
    void DoTheThing() {
       var queue = new Queue<B>();
       foreach (var b in _theList)
           queue.Enqueue(b);
       while (queue.Count != 0)
       {
           var b = queue.Dequeue();
           b.ProcessThisLevelOnly();
           // now we do the logical recursion here
           foreach (var inner in b.Items)
               queue.Enqueue(inner);
       }
    }
}

You can use a stack vs queue depending on depth-first or breadth-first.