swift 创建栈(stack)

/// 栈
// 用数组作为栈的线性表的实现
public struct Stack<T> {
    // 数组
    fileprivate var stackArray = [T]()
    
    // count
    public var count: Int {
        return stackArray.count
    }
    
    // 是否为空
    public var isEmpty: Bool {
        return stackArray.isEmpty
    }
    
    // 顶部元素
    public var top: T? {
        guard !isEmpty else {
            return nil
        }
        return stackArray.last
    }
    
    // push 操作
    public mutating func push(_ element: T) {
        stackArray.append(element)
    }
    
    // pop 操作
    public mutating func pop() -> T? {
        guard !isEmpty else {
            print("stack is empty")
            return nil
        }
        return stackArray.removeLast()
    }
    
    // 打印所有元素
    public mutating func printAllElement() {
        guard count > 0 else {
            print("stack is empty")
            return
        }
        print("npint all stack elements")
        for (index, value) in stackArray.enumerated() {
            print("[(index)](value)")
        }
    }
}

var stack = Stack.init(stackArray: [])
stack.printAllElement()
stack.isEmpty
stack.push(22)
stack.printAllElement()
stack.push(33)
stack.printAllElement()
stack.top
stack.pop()
stack.printAllElement()
stack.pop()
stack.printAllElement()
stack.isEmpty