Generic swift queue

Queue.swift

private class QueueItem<T> {
	let value: T!
	var next: QueueItem?

	init(_ newvalue: T?) {
		self.value = newvalue
	}
}

public class Queue<T> {

	typealias Element = T

	private var front: QueueItem<Element>
	private var back: QueueItem<Element>

	public init() {
		back = QueueItem(nil)
		front = back
	}

	public func enqueue(value: Element) {
		back.next = QueueItem(value)
		back = back.next!
	}

	public func dequeue() -> Element? {
		if let newhead = front.next {
			front = newhead
			return newhead.value
		} else if let value = front.value {
			empty()
			return value
		} else {
			return nil
		}
	}

	public func peek() -> Element? {
		return front.next?.value
	}

	public func isEmpty() -> Bool {
		return front === back
	}

	public func empty() {
		back = QueueItem(nil)
		front = back
	}
}