如何使这个Stack结构定义？

Question

I want to make this Stack struct properly.

How can I define ' topItem '?

Is it right to show above " newstack "?

    struct Stack {
    var Items:[String] = []



    mutating func push (item:String){
        Items += [item]
    }

    mutating func pop() -> String {
        return Items.removeLast()
    }

    var topItem =`enter code here`

    }

var newStack = Stack()

newStack.push("HistoryListController")
newStack.push("HistoryDetailViewController")
newStack.push("HistoryTimelineViewController")
newStack.push("HistoryChartViewController")

newStack.Items


if let topVC = newStack.topItem {
    print("Top View Controller is \(topVC)")
    //HistoryChartViewController
}

newStack.pop()

if let topVC = newStack.topItem {
    print("Top View Controller is \(topVC)")
    //HistoryTimelineViewController
}

I'm very beginner in Swift. This is my first code

Answer 1

First, items should be lowercase. Second, it's not clear what you want topItem to return. If you want the most recent object, you could implement it like this:

struct Stack {
    var items = [String]()

    mutating func push (item:String){
        items += [item]
    }

    mutating func pop() -> String {
        let result = items[0]
        items.removeLast()
        return result
    }

    var topItem : String? {
        return items.last
    }

}

var newStack = Stack()

newStack.push("HistoryListController")
newStack.push("HistoryDetailViewController")
newStack.push("HistoryTimelineViewController")
newStack.push("HistoryChartViewController")

newStack.topItem // "HistoryChartViewController"

newStack.items

If you want the first object, change it to return items.first .