This is the demonstration of Stack in Swift. I have used the default functions to handle the Stack operations.

StackPlayground.playground

//: Playground - noun: a place where people can play

import Foundation

class Stack {
    static let list = Stack.init()
    private var items = Array<Any>()
    internal var limit = 5
    
    //MARK: Push
    internal func push(item: Any) -> Void {
        if isReachesToMaxLimit() {
            print("Stack reaches to the maximum limit \(limit). Couldn't insert >>>\(item)<<<")
            return
        }
        items.append(item)
    }
    
    //MARK: Pop
    internal func pop() -> Any? {
        guard !isEmptyList(showMessage: true) else {
            return nil
        }
        return items.removeLast()
    }
    
    internal func pop(completion: (Any)->()) {
        if !isEmptyList(showMessage: true) {
            completion(items.removeLast())
        }
    }
    
    //MARK: Get Items
    internal func getItems() -> Array<Any>? {
        
        if isEmptyList(showMessage: true) {
            return nil
        }
        
        print("------------------------------------------------------------------------------------------------------------------")
        print("Items in Stack")
        print("------------------------------------------------------------------------------------------------------------------")
        
        items.forEach { (item) in
            print(item)
        }
        
        return items
    }
    
    //MARK: Validators
    private func isEmptyList(showMessage: Bool) -> Bool {
        if items.isEmpty {
            if showMessage {
                print("Stack is empty.")
            }
            return true
        }
        return false
    }
    
    private func isReachesToMaxLimit() -> Bool {
        if !isEmptyList(showMessage: false) {
            if items.count >= limit {
                return true
            }
        }
        return false
    }
    
//    //MARK: Search Item
//    internal func search(item searchItem: Any) -> Bool {
//        if isEmptyList(showMessage: true) {
//            return false
//        }
//
//        items.contains { (item) -> Bool in
//            if searchItem == item {
//                return true
//            }
//        }
//
//        return false
//    }
}

//Usage - Push
Stack.list.push(item: "A")
Stack.list.push(item: "B")
Stack.list.push(item: "C")
Stack.list.push(item: "D")
Stack.list.push(item: "E")

//Usage - List Items
Stack.list.getItems()

Stack.list.push(item: "F")

Stack.list.pop { (item) in
    print(">>>\(item)<<< is popped.")
}