LinkedList.swift

final class Node<Value>: Sequence {
  typealias NextNode = Node<Value>?

  let value: Value
  var next: NextNode

  init(value: Value, nextNode: NextNode = nil) {
    self.value = value
    self.next = nextNode
  }

  private struct NodeIterator: IteratorProtocol {
    var head: NextNode

    mutating func next() -> Value? {
      let value = self.head?.value
      self.head = self.head?.next
      return value
    }
  }
  
  func makeIterator() -> some IteratorProtocol {
    return NodeIterator(head: self)
  }
}