Stack and Generics implementation in Swift 3.1

Stack-Generics.swift

import UIKit

// Stack and Generics implementation in Swift 3.1

class Node<T> {
    let value: T
    var nextNode: Node<T>?
    var prevNode: Node<T>?
    
    init(value: T) {
        self.value = value
    }
}

class Stack<T> {
    
    var top: Node<T>?
    
    func push(_ value: T) {
        let oldTop = top
        top = Node(value: value)
        top?.nextNode = oldTop
    }
    
    func pop() -> T? {
        let currentTop = top
        top = top?.nextNode
        return currentTop?.value
    }
    
    func peek() -> T? {
        return top?.value
    }
}

let stack = Stack<Int>()
stack.push(12)
stack.push(22)
stack.push(32)

stack.pop()
stack.pop()
stack.pop()
stack.pop()


struct Users {
    let name: String
    let userName: String
}

let me = Users(name: "Ashish", userName: "@Kapoor")
let you = Users(name: "You", userName: "@You")

let usersStack = Stack<Users>()

usersStack.push(me)
usersStack.push(you)


print(usersStack.peek()?.name ?? "")
print(usersStack.peek()?.userName ?? "")