As a printf debugger, I have a little trick I like to use when logging hierarchy function calls. For example:

struct Node {
    var name: String
    var children = [Node]()

    init(_ name: String) {
        self.name = name
    }
    mutating func addChild(child: Node) {
        children.append(child)
    }
    func printHierarchy() {
        print("\(name)")
        for each in children {
            each.printHierarchy()
        }
    }
}

var root = Node("Topmost")
var n1 = Node("n1")
var n2 = Node("n2")
var n3 = Node("n3")
var n4 = Node("n4")
n3.addChild(child: n4)
n2.addChild(child: n3)
root.addChild(child: n1)
root.addChild(child: n2)

root.printHierarchy()

This prints:

Topmost
n1
n2
n3
n4

which isn't that useful. But if we modify printHierarchy() to add an indent argument with a default value of 0:

func printHierarchy(indent: Int=0) {
    print("\(String(repeating: "  ", count: indent))\(name)")
    for each in children {
        each.printHierarchy(indent: indent + 1)
    }
}

Our output becomes:

Topmost
  n1
  n2
    n3
      n4

This is especially useful when we are logging more information in each node to debug method calls up and down the hierarchy.