Generics.swift

  
  struct Queue<Element> {
    
    private var elements: [Element] = []
    var description: String {
        return "Your queue has \(elements.count) items: \(elements)"
    }
    
    mutating func enqueue(newElement: Element) {
        elements.append(newElement)
    }
    
    mutating func dequeue() -> Element? {
        guard !elements.isEmpty else { return nil }
        
        return elements.remove(at: 0)
        
    }
}

var intQueue = Queue<Int>()

intQueue.enqueue(newElement: 2)
intQueue.enqueue(newElement: 20)
intQueue.description

var stringQueue = Queue<String>()

stringQueue.enqueue(newElement: "Hello world")
stringQueue.enqueue(newElement: "How are you?")

stringQueue.description
stringQueue.dequeue()
stringQueue.description