IndirectectEnum.swift

import Foundation

// Indirect enums are enums that need to reference themselves somehow, 
// and are called “indirect” because they modify the way Swift stores them so they can grow to any size. 
// Without the indirection, any enum that referenced itself could potentially become infinitely sized: 
// it could contain itself again and again, which wouldn’t be possible

indirect enum LinkedListItem<T> {
    case endNode(value: T)
    case nextNode(value: T, next: LinkedListItem)
}

let third = LinkedListItem.endNode(value: "third")
let second = LinkedListItem.nextNode(value: "second", next: third)
let first = LinkedListItem.nextNode(value: "first", next: second)

var currentNode = first

whileLoop : while true {
    switch currentNode {
    case .endNode(value: let value):
        print(value)
        break whileLoop
    case .nextNode(value: let value, next: let nextItem):
        print(value)
        currentNode = nextItem
    }
}