func swap(_ nums: inout [Int], _ p: Int, _ q: Int) {
 let temp = nums[p]
 nums[p] = nums[q]
 nums[q] = temp 
}

func swap<T>(_ nums: inout [T], _ p: Int, _ q: Int) {
 let temp = nums[p]
 nums[p] = nums[q]
 nums[q] = temp 
}

func swap<T>(_ nums: inout [T], _ p: Int, _ q: Int) {
 (nums[p], nums[q]) = (nums[q], nums[p])
}

public class Node {
 public var value: Int
 public var prev: Node?
 public var post: Node?

 public init(_ value: Int) {
 self.value = value
 }
}

let head = Node(0)
let tail = Node(1)
head.post = tail
tail.prev = head

func addTwo(_ num: Int) -> Int {
 return num + 2
}

func addFour(_ num: Int) -> Int {
 return num + 4
}

func add(_ num: Int) -> (Int) -> Int {
 return { val in
 return num + val
 }
}

let addTwo = add(2), addFour = add(4), addSix = add(6), addEight = add(8)

func divide(dividend: Double?, by divisor: Double?) -> Double? { 
 if dividend == nil { 
 return nil 
 } 
 if divisor == nil { 
 return nil 
 } 
 if divisor == 0 { 
 return nil
 } 
 return dividend! / divisor!
}

func divide(dividend: Double?, by divisor: Double?) -> Double? { 
 guard let dividend = dividend, let divisor = divisor, divisor != 0 else {
 return nil
 }

 return dividend / divisor
}

var car = "Benz" 
let closure = { [car] in 
 print("I drive \(car)")
} 
car = "Tesla" 
closure()

var car = "Benz" 
let closure = {
 print("I drive \(car)")
} 
car = "Tesla" 
closure()

protocol Pizzeria { 
 func makePizza(_ ingredients: [String])
 func makeMargherita()
} 

extension Pizzeria { 
 func makeMargherita() { 
 return makePizza(["tomato", "mozzarella"]) 
 }
}

struct Lombardis: Pizzeria { 
 func makePizza(_ ingredients: [String]) { 
 print(ingredients)
 } 
 func makeMargherita() {
 return makePizza(["tomato", "basil", "mozzarella"]) 
 }
}

let lombardis1: Pizzeria = Lombardis()
let lombardis2: Lombardis = Lombardis() 
lombardis1.makeMargherita()
lombardis2.makeMargherita()

["tomato", "basil", "mozzarella"]
["tomato", "basil", "mozzarella"]

protocol Pizzeria {
 func makePizza(_ ingredients: [String])
}

extension Pizzeria {
 func makeMargherita() {
 return makePizza(["tomato", "mozzarella"])
 }
}

struct Lombardis: Pizzeria {
 func makePizza(_ ingredients: [String]) {
 print(ingredients)
 }
 func makeMargherita() {
 return makePizza(["tomato", "basil", "mozzarella"])
 }
}

let lombardis1: Pizzeria = Lombardis()
let lombardis2: Lombardis = Lombardis()
lombardis1.makeMargherita()
lombardis2.makeMargherita()

["tomato", "mozzarella"]
["tomato", "basil", "mozzarella"]

const int number = 0;

let number = 0

class A {
 var val = 1
}

var a = A()
var b = a
b.val = 2

struct A {
 var val = 1
}

var a = A()
var b = a
b.val = 2