Queue with Array

queue_with_array.swift

struct Queue <Element> {
    var head: Int = 0
    var tail: Int = 0
    var size: Int = 0
    let data:UnsafeMutableBufferPointer<Element>

    init(size: Int) {
        self.data = UnsafeMutableBufferPointer<Element>.allocate(capacity: size+1)
        self.size = size + 1
    } 

    var isEmpty: Bool {
        return head == tail
    }

    var isFilled: Bool {
        return head == (tail + 1) % self.size
    }

    mutating func enqueue(_ element: Element) {
        precondition(self.isFilled == false)
        self.data[tail] = element
        tail = (tail + 1) % self.size
    }

    @discardableResult
    mutating func dequeue() -> Element {
        precondition(self.isEmpty == false)
        defer { self.head = (self.head + 1) % self.size }
        return self.data[head]
    }
}