The document discusses several new features introduced in Swift 4 including multi-line string literals, improvements to strings and collections, private access control, smart keypaths, existentials, one-sided ranges, and limiting automatic @objc inference. It also introduces the Codable protocol for encoding and decoding types to and from data, which provides a standard way to serialize and deserialize objects to formats like JSON.

1. letswift(17)
What’s New in Swift 4
Fancy김영후

2. letswift(17)
What’s New in Swift 4

3. letswift(17)
What’s New in Swift 3 ?

4. letswift(17)
What’s New in Swift 2 ?

5. letswift(17)
What’s New in Swift 1.2 ?

6. Swift 1.2
if let data = dataStream.data {
if let encoding = data.encoding {
//Swift 1.0
}
}
if let data = dataStream.data, let encoding = data.encoding
where somethingTrue {
//Swift 2.0
}
}

7. Swift 2
guard let frog = frog, let cow = cow else {
return
}
extension MyViewController: UITableViewDataSource {
//implement UITableViewDataSource
}

8. Swift 2
enum DrinkError: ErrorType {
case NoBeerRemainingError
}
func drinkWithError() throws {
if beer.isAvailable() {
} else {
throw DrinkError.NoBeerRemainingError
}
}
do {
try drinkWithError()
} catch {
print(error)
}

9. Swift 3
helloString.stringByAppendingString("world")
helloString.appending("world")
UIColor.blueColor().colorWithAlphaComponent(0.5)
UIColor.blue.withAlphaComponent(0.5)
NSBundle.mainBundle()
Bundle.main
numbers.maxElement()
numbers.max()
animals.insert("Koala", atIndex: 0)
animals.insert("Koala", at: 0)
WKInterfaceDevice.currentDevice()
WKInterfaceDevice.current()
device.playHaptic(.success)
device.play(.success)

10. Swift 3
UIStatusBarStyle.LightContent
UIStatusBarStyle.lightContent
SKLabelVerticalAlignmentMode.Center
SKLabelVerticalAlignmentMode.center
Optional<String>.None
Optional<String>.none

11. letswift(17)
What’s New in Swift 4

12. letswift(17)
Multi-Line String Literals

13. Multi-Line Literals
let message = """
이것은
멀티라인
문자열
“""
//let single = """이것은 불가능"""

14. Multi-Line Literals
let single2 = """
이것은
싱글라인
"""

15. Multi-Line Literals
let indentation = """
1
2
3
"""
// 1n 2n 3
let indentation = """
1
2
3
"""
//1n2n3

16. Multi-Line Literals
let indentation = """
1
2
3
“""
//Error: change indentation of this line to match closing
delimiter
let indentation = """
1
2
3
"""

17. letswift(17)
String

18. Collections once again
let string = "abcdefg"
print(string.characters.count)
print(string.count)
let cow = "Cow 🐮"
for char in cow {
print(char)
}
cow.count // 5
cow.isEmpty // false
cow.dropFirst() // "ow 🐮"
String(cow.reversed()) // "🐮 owC”

19. Unicode 9
""".count // Now: 1, Before: 2
"#".count // Now: 1, Before: 2
"$".count // Now: 1, Before, 4

20. Substring, StringProtocol
protocol StringProtocol : BidirectionalCollection {
// Implementation detail as described above
}
extension String : StringProtocol,
RangeReplaceableCollection {
typealias SubSequence = Substring
subscript(bounds: Range<String.Index>) -> Substring {
...
}
}
struct Substring : StringProtocol,
RangeReplaceableCollection {
typealias SubSequence = Substring
// near-identical API surface area to String
}

21. Substring, StringProtocol
let endIndex = cow.index(cow.startIndex, offsetBy: 2)
var cowSubstring = cow[cow.startIndex...endIndex]
type(of: cowSubstring) // Substring.Type
// Concatenate a String onto a Substring
cowSubstring += "🥛" // "Milk🥛"
// Create a String from a Substring
let milkString = String(cowSubstring) // "Milk🥛"

22. letswift(17)
Private

23. private, fileprivate
class Person {
private let name: String
init(name: String, age: Int) {
self.name = name
}
}
extension Person: CustomStringConvertible {
var description: String {
//Swift 3에선 fileprivate로 해야 컴파일 가능
return "(self.name)"
}
}

24. fileprivate in Swift 3
Extension Oriented Programming을 밀면서
fileprivate이 사실상 private 역할을 하게 됨
Swift3 private은 extension에서 접근 하지 못하는 필
드들을 구분할 수 있으나 과연 의미가 있는 구분인가?
Swift4 private “같은 소스 파일”에 있는 extension은
private 필드에 접근 가능함

25. fileprivate in Swift 4.0
class Person {
fileprivate var name: String
init(name: String) {
self.name = name
}
}
func run() {
let p = Person(name: "Younghoo")
p.name = "0hoo"
//fileprivate 필드는 같은 파일에서 접근 가능
}

26. letswift(17)
Smart KeyPaths

27. KeyPaths
struct Person {
var name: String
}
struct Book {
var title: String
var authors: [Person]
var primaryAuthor: Person {
return authors.first!
}
}
let abelson = Person(name: "Harold Abelson")
let sussman = Person(name: "Gerald Jay Sussman")
let book = Book(title: "Structure and Interpretation of
Computer Programs", authors: [abelson, sussman])

28. KeyPaths
book[keyPath: Book.title]
//"Structure and Interpretation of Computer Programs"
book[keyPath: Book.primaryAuthor.name]
//"Harold Abelson”
let authorKeyPath = Book.primaryAuthor
let nameKeyPath = authorKeyPath.appending(path: .name)
book[keyPath: nameKeyPath]
//"Harold Abelson"

29. KVO
import Foundation
class Child: NSObject {
let name: String
// KVO-enabled properties must be @objc dynamic
@objc dynamic var age: Int
init(name: String, age: Int) {
self.name = name
self.age = age
super.init()
}
func celebrateBirthday() {
age += 1
}
}

30. KVO, KeyPaths
let eugene = Child(name: "Eugene", age: 0)
let observation = eugene.observe(.age, options: [.initial, .old]) {
(child, change) in
if let oldValue = change.oldValue {
print("(child.name)’s age changed from (oldValue) to (child.age)")
} else {
print("(child.name)’s age is now (child.age)")
}
}
//Eugene’s age is now 0
eugene.celebrateBirthday()
//Eugene’s age changed from 0 to 1

31. 옛날 옛적에…
//Objective-C
[self.controller addObserver:self forKeyPath:@"isEnabled"
options:NSKeyValueObservingOptionNew context:nil];
[self addObserver:self forKeyPath:@"controller.isEnabled"
options:NSKeyValueObservingOptionNew context:nil];
//Swift 2
addObserver(self, forKeyPath: "isEnabled", options: [],
context: nil)
//Swift 3
addObserver(self, forKeyPath: #keyPath(isEnabled), options:
[.old, .new], context: nil)

32. letswift(17)
Existentials

33. 1.
(격식) (인간의) 존재에 관한[관련된]
2.
(철학) 실존주의적인

34. Existentials
protocol Saveable {
func save()
}
protocol Loadable {
func load()
}
func doThing(thing: protocol<Saveable, Loadable>) {
thing.save()
thing.load()
}

35. Swift 3 SE-0095
func doThing(thing: Saveable & Loadable) {
thing.save()
thing.load()
}
func secondFunc<T : Saveable & Loadable>(x: T) {
}

36. Class and subtype
func reload(view: UIView & Reloadable) {
}

37. letswift(17)
One-Sided Ranges

38. One-Sided Ranges
let planets = ["Mercury", "Venus", "Earth", "Mars",
"Jupiter", "Saturn", "Uranus", “Neptune"]
let outsideAsteroidBelt = planets[4...]
// Before: planets[4..<planets.endIndex]
let firstThree = planets[..<4]
// Before: planets[planets.startIndex..<4]

39. Pattern Matching
func temperature(planetNumber: Int) {
switch planetNumber {
case ...2: // anything less than or equal to 2
print("더워")
case 4...: // anything greater than or equal to 4
print("추워")
default:
print("좋아")
}
}
temperature(planetNumber: 3)

40. letswift(17)
Limiting @objc inference

41. @objc
Objective-C에 노출되는 코드는 @objc가 필요
Swift3에서 자동으로 추론함
• 사용자가 @objc를 원하는지 알기 어려움
• 컴파일러가 메타데이터를 생성해야 함
• 6~8%의 바이너리 사이즈 증가

42. @objc
이제 자동으로 추론되지 않는다
여전히 추론되는 예외
class Super {
@objc func foo() { }
}
class Sub : Super {
/* inferred @objc */
override func foo() { }
}

43. @objc
@objc protocol MyDelegate {
func bar()
}
class MyClass : MyDelegate {
/* inferred @objc */
func bar() { }
}
@IBAction, @IBOutlet, @NSManaged,
@IBInspectable 등

44. @objc
dynamic은 더 이상 자동으로 추론되지 않음
class MyClass {
dynamic func foo() { }
// error: 'dynamic' method must be '@objc'
@objc dynamic func bar() { } // okay
}
???
dynamic이 추후에 Objective-C 런타임과 떨어질 수 있다고 함
- (SE-0160)

45. letswift(17)
Codable

46. Before Swift4
struct Todo {
var id: Int?
var title: String
var userId: Int
var completed: Bool
}

47. Before Swift4
struct Todo {
var id: Int?
var title: String
var userId: Int
var completed: Bool
init?(json: [String: Any]) {
guard let title = json["title"] as? String,
let id = json["id"] as? Int,
let userId = json["userId"] as? Int,
let completed = json["completed"] as? Bool else {
return nil
}
self.title = title
self.userId = userId
self.completed = completed
self.id = id
}
}

48. Codable
struct Todo: Codable {
var id: Int?
var title: String
var userId: Int
var completed: Bool
}

49. Codable
let dict = [
"id": 1, "title":
"Let's Swift 준비",
"userId": 1,
"completed": false
] as [String: Any]
do {
let data = try JSONSerialization.data(withJSONObject: dict, options: .prettyPrinted)
let todo = try JSONDecoder().decode(Todo.self, from: data)
print(todo.title)
} catch {
}

50. Before Swift4
struct Todo {
var id: Int?
var title: String
var userId: Int
var completed: Bool
func toJSON() -> [String: Any] {
var json = [String: Any]()
json["title"] = title
json["userId"] = userId
json["completed"] = completed
if let id = id {
json["id"] = id
}
return json
}
}

51. Before Swift4
let urlRequest = URLRequest(url: URL(string: “http://
letswift/api")!)
do {
let jsonTodo = try
JSONSerialization.data(withJSONObject: todo.toJSON(),
options: [])
urlRequest.httpBody = jsonTodo
}

52. Codable
let urlRequest = URLRequest(url: URL(string: “http://
letswift.com/api")!)
let encoder = JSONEncoder()
do {
let todo = Todo(id: nil, title: "Let's Swift 준비",
userId: 1, completed: false)
let json = try encoder.encode(todo)
urlRequest.httpBody = json
} catch {
}

53. Nested, Codable
struct Address: Codable {
let city: String
let zipcode: String
}
struct User: Codable {
let id: Int?
let name: String
let email: String
let address: Address
}

54. Decodable
struct Developer: Decodable {
let id: Int
let fullName: String
let iOS: Bool
}
let json = """
{
"id": 123456,
"fullName": "Kim Younghoo",
"iOS": false
}
""".data(using: .utf8)!
let dev = try JSONDecoder().decode(Developer.self, from:
json)
print(dev)

55. https://developer.apple.com/documentation/swift/
decodable

57. init(from: Decoder) Required???

58. Compiler Magic!

59. Decodable
struct Developer {
let id: Int
let fullName: String
let iOS: Bool
}
extension Developer: Decodable {
enum DeveloperKeys: String, CodingKey {
case fullName
case id
case iOS
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: DeveloperKeys.self)
let fullName: String = try container.decode(String.self,
forKey: .fullName)
let id: Int = try container.decode(Int.self, forKey: .id)
let iOS: Bool = try container.decode(Bool.self, forKey: .iOS)
self.init(id: id, fullName: fullName, iOS: iOS)
}
}

60. Array
let json = """
[{
"fullName": "Kim Younghoo",
"id": 123,
"iOS": true,
},{
"fullName": "Yoo Yongha",
"id": 789,
"iOS": false,
}]
""".data(using: .utf8)!
let structArray = try
JSONDecoder().decode([Developer].self, from: json)
structArray.forEach { print($0) }

61. Dictionary
let json = """
{
"one": {
"fullName": "Kim Younghoo",
"id": 123,
"iOS": true,
},
"two": {
"fullName": "Yoo Yongha",
"id": 789,
"iOS": false,
}
}
""".data(using: .utf8)!
let dict = try JSONDecoder().decode([String: Developer].self,
from: json)
dict.forEach { print($0) }

62. Change Key Names
struct Developer: Decodable {
let id: Int
let fullName: String
let iOS: Bool
private enum CodingKeys: String, CodingKey {
case id = "developer_id"
case fullName
case iOS = "is_iOS"
}
}
let json = """
{
"developer_id": 123456,
"fullName": "Kim Younghoo",
"is_iOS": false
}
""".data(using: .utf8)!
let dev = try JSONDecoder().decode(Developer.self, from: json)

63. Play with “Using JSON with Custom Types”
Playground

64. letswift(17)
Swift 5.0

65. Swift 5.0
Late 2018
Rust-inspired memory ownership model
Syntactic additions
Groundwork for a new concurrency model
• Non-goal for Swift 5
• maybe async/await

66. 감사합니다