The document discusses various idioms in Swift including optional binding with guard let and if let, nil coalescing operator, switch statements with optionals and associated values, closures, lazy properties, and computed properties with property observers. Key idioms covered include using guard let to ensure non-nil arguments, extracting associated values from enums using switch, initializing immutable variables with closures, and updating for loops to the Swift 3 syntax.

1. Idioms in Swift
Kaz Yoshikawa
May 2016

2. About me

3. Kaz Yoshikawa
• Electricwoods LLC 代表 / Digital Lynx Systems Inc. 副代表
• e-mail: kaz@digitallynx.com
• LinkedIn: https://www.linkedin.com/in/kazyoshikawa
• Working History
• Adobe Systems (Tokyo)
• Lionbridge (Tokyo)
• Quark (Tokyo / Denver)
• Hummingbird Communications (Mt. View, USA)
• Fact International (Vancouver, Canada)
• Perle Systems (Toronto, Canada), etc.

4. Engineering

5. 将棋盤Kit

6. What is Idiom?

7. Optional

8. guard let
• 二つの引数が nil でない事を保証する
func add(a: Int?, _ b: Int?) -> Int? {
guard let a = a, let b = b else { return nil }
return a + b
}

9. if let
• if let を使う
func add(a: Int?, _ b: Int?) -> Int? {
if let a = a, let b = b {
return a + b
}
return nil
}

10. where
• guard let で０以上を保証する
func add(a: Int?, _ b: Int?) -> Int? {
guard let a = a, let b = b where a >= 0 && b >= 0 else {
return nil
}
return a + b
}
• if let でも０以上を保証する
func add(a: Int?, _ b: Int?) -> Int? {
if let a = a, let b = b where a >= 0 && b >= 0 {
return a + b
}
return nil
}

11. nil-coalescing Operator
• nil の場合は 0 として扱う
func add(a: Int?, b: Int?) -> Int {
return (a ?? 0) + (b ?? 0)
}

12. Switch

13. Optional in Switch
• 実は optional も switch 文に使える
func countryName(identifier: String?) -> String? {
switch identifier {
case "JP"?: return "Japan"
case "GB"?: return "England"
case "US"?: return "U.S.A."
default: return nil
}
}

14. Late Initializing
Immutable Variables
• 初期値を後で設定する不定変数
let color: UIColor // "= value"
switch value % 3 {
case 0: color = UIColor.whiteColor()
case 1: color = UIColor.redColor()
default: fatalError()
}
• 初期化しないケースがあると、コンパイルエラー

15. Complex switch cases
for thing in things {
switch thing {
case 0 as Int:
print("zero as an Int")
case 0 as Double:
print("zero as a Double")
case let someInt as Int:
print("an integer value of (someInt)")
case let someDouble as Double where someDouble > 0:
print("a positive double value of (someDouble)")
case is Double:
print("some other double value")
case let someString as String:
print("a string value of "(someString)"")
case let (x, y) as (Double, Double):
print("an (x, y) point at (x), (y)")
case let movie as Movie:
print("Movie:'(movie.name)'")
default:
print("something else")
}
}

16. Implicitly
Unwrapped Optional

17. Implicitly Unwrapped
Optional with if statement
• Implicitly Unwrapped Optional でも if let は 使える
let a: Int!
if let a = a {
print("(a)")
}

18. Implicitly Unwrapped Optional
with guard statement
• Implicitly Unwrapped Optional でも guard は 使える
class MyObject {
var value: Int! = nil
func some() {
guard let value = value else { return }
print("(value)")
}
func other() {
guard value != nil else { return }
print("(value)")
}
}

19. Associated Values

20. Defining Associated
Value
enum Element {
case String(Swift.String)
case Boolean(Bool)
case Integer(Int)
case Float(Swift.Float)
case Dictionary([Swift.String: Element])
case Array([Element])
case Null
}
let integer = Element.Integer(42)
let city = Element.String("Tokyo")
let cities = Element.Array([city])
let dictionary = Element.Dictionary(["items": array])

21. Extracting Associated Values
Using switch Statement
• Associated Value を Switch文で取り出す
switch element {
case .String(let string): print("string: (string)")
case .Boolean(let value): print("boolean: (value)")
case .Integer(let value): print("ineteger: (value)")
case .Float(let value): print("float: (value)")
case .Dictionary(let dictionary):
print("dictionary: (dictionary)")
case .Array(let array): print("array: (array)")
case .Null: print("null")
}

22. Extracting Associated
Values using if Statement
• If 文でも取り出せます
let element1: Element = …
if case .String(let string) = element1 {
print("(string)")
}
• Optional な場合でも取り出せます
let element: Element? = …
if case .String(let string)? = element1 {
print("(string)")
}

23. Extracting Associated
Values
• division -> members -> person -> name
let name = Element.String("John")
let john = Element.Dictionary(["name": name])
let members = Element.Array([john])
let group = Element.Dictionary(["members": members])
• 一発で取り出せる
if case .Dictionary(let group) = group,
case .Array(let members)? = division["members"],
case .Dictionary(let member)? = members.first,
case .String(let name)? = member["name"] {
print("(name)") // John
}

24. Closure

25. Basic Closure
class MyViewController: UIViewController {
var state: Bool = false
func toggle(animated: Bool) {
let closure = {
self.view.backgroundColor = self.state ?
UIColor.redColor() : UIColor.whiteColor()
self.state = !self.state
}
if animated {
UIView.animateWithDuration(0.3) {
closure() // <-- Here!!
}
}
else {
closure() // <-- Here!!
}
}
}

26. Basic Closure
class MyViewController: UIViewController {
var state: Bool = false
func toggle(animated: Bool) {
let closure = {
self.view.backgroundColor = self.state ?
UIColor.redColor() : UIColor.whiteColor()
self.state = !self.state
}
if animated {
UIView.animateWithDuration(0.3) {
closure() // <-- Here!!
}
}
else {
closure() // <-- Here!!
}
}
}

27. Execute on Main Thread
func dispatch_sync_main(block: () -> Void) {
if NSThread.isMainThread() {
block()
}
else {
dispatch_sync(dispatch_get_main_queue()) { () ->
Void in
block()
}
}
}
dispatch_sync_main {
self.tableView.reloadData()
}

28. Execute on Main Thread
func dispatch_sync_main(block: () -> Void) {
if NSThread.isMainThread() {
block()
}
else {
dispatch_sync(dispatch_get_main_queue()) { () ->
Void in
block()
}
}
}
dispatch_sync_main {
self.tableView.reloadData()
}

29. Execute on Main Thread
func dispatch_sync_main(block: () -> Void) {
if NSThread.isMainThread() {
block()
}
else {
dispatch_sync(dispatch_get_main_queue()) { () ->
Void in
block()
}
}
}
dispatch_sync_main {
self.tableView.reloadData()
}

30. Initialize Immutable
Variable Using Closure
• closure と switch 文を使うとかっこよく書ける
let color: UIColor = {
switch value % 2 {
case 0: return UIColor.whiteColor()
case 1: return UIColor.redColor()
default: fatalError()
}
}() // "()" !!

31. Initialize Immutable
Variable Using Closure
• closure と switch 文を使うとかっこよく書ける
let color: UIColor = {
switch value % 2 {
case 0: return UIColor.whiteColor()
case 1: return UIColor.redColor()
default: fatalError()
}
}() // "()" !!

32. Changing Behavior with
Using Closure
typealias DrawingHandler = (UIPanGestureRecognizer)->()
class MyView: UIView {
func panGesture(sender: UIPanGestureRecognizer) {
self.drawingHandler(sender)
}
var drawingHandler: DrawingHandler!
let ovalGesture: DrawingHandler = { gesture in
// draw oval
}
let rectangleGesture: DrawingHandler = { gesture in
// draw rectangle
}
}

33. Changing Behavior with
Using Closure
typealias DrawingHandler = (UIPanGestureRecognizer)->()
class MyView: UIView {
func panGesture(sender: UIPanGestureRecognizer) {
self.drawingHandler(sender)
}
var drawingHandler: DrawingHandler!
let ovalGesture: DrawingHandler = { gesture in
// draw oval
}
let rectangleGesture: DrawingHandler = { gesture in
// draw rectangle
}
}

34. lazy

35. When should I use lazy?
• 処理が重くて初期化時に実行するのは不都合
• 大人の理由で init で初期化できないプロパティ

36. Using lazy var
class MyObject {
lazy var path: String = {
return NSBundle.mainBundle()
.pathForResource("text", ofType: "txt")!
}()
lazy var text: String = {
return try! String(contentsOfFile: self.path)
}()
}

37. Initializing code per
instance
• 何回呼ばれてもインスタンス毎に一度のみ初期化するコード
class MyView: UIView {
override func layoutSubviews() {
print("MyView: (#function)")
super.layoutSubviews()
setup()
}
private lazy var setup: (()->()) = {
print("MyView: (#function)")
// さまざまな初期化のコード
return {}
}()
}
http://qiita.com/codelynx/items/f0243d631f2448e8

38. Singleton

39. Singleton
• 典型的なシングルトン
class Manager {
static let sharedManager = Manager()
private init() {
}
}
• クロージャーを使ったシングルトン
class Manager {
static var sharedManager: Manager = {
return Manager()
}()
private init() {
}
}
http://qiita.com/codelynx/items/a936afe0a45d4cf5abfb

40. Updating C style
`for` statement
http://qiita.com/codelynx/items/899c26dd2cbdba7d2b00

41. for var i = 0 ; i < 100 ; i++
// C-Style for statement
for var i = 0 ; i < 100 ; i++ {
print("(i)")
}
// Swift 3.0 ready
(0 ..< 100).forEach { print("($0)") }
// Swift 3.0 ready
for i in (0 ..< 100) {
print("(i)")
}

42. for var i = 99 ; i >= 0 ; i--
// C-Style for statement
for var i = 99 ; i >= 0 ; i-- {
print("(i)")
}
// Swift 3.0 ready
(0 ..< 100).reverse().forEach { print("($0)") }
// Swift 3.0 ready
for i in (0 ..< 100).reverse() {
print("(i)")
}

43. for var i = 0; i < 100 ; i += 2
// C-Style for statement
for var i = 0; i < 100 ; i += 2 {
print("(i)")
}
// Swift 3.0 ready
0.stride(to: 100, by: 2).forEach { print("($0)") }

44. for var i = 98 ; i >= 0 ; i -=
2
// C-Style for statement
for var i = 98 ; i >= 0 ; i -= 2 {
print("(i)")
}
// Swift 3.0 ready
98.stride(through: 0, by: -2).forEach { print("($0)") }
// Swift 3.0 ready
0.stride(to: 100, by: 2).reverse().forEach { print("($0)") }
// Swift 3.0 ready
for i in 0.stride(to: 100, by: 2).reverse() {
print("(i)")
}

45. for without increment
• 次の再初期化式の指定がなく、刻みが不定の場合
// C-Style for statement
for var i = 0 ; i < 100 ; {
print("(i)")
if (i * i) % 2 == 0 { i += 1 }
else { i += 2 }
}
// Swift 3.0 ready
var i = 0
while i < 100 {
print("(i)")
if (i * i) % 2 == 0 { i += 1 }
else { i += 2 }
}

46. Computed Properties
and Property Observer

47. Custom Property
class MyObject {
private var _name: String = ""
var name: String {
get { return _name }
set { _name = newValue }
}
}

48. Property Observer
class MyView: UIView {
var name: String = "" {
didSet {
self.setNeedsLayout()
}
}
}

49. Wrap Up

50. Wrap up
• 知っていても、0.2秒で思い出せない記法はいろいろあ
る
• Open Source を散策して先人達の記法を参考に
• 気がついた記法があれば、playground などにメモ
• 時々、swift 文法書を眺め直してみよう

51. Thank You
Kaz Yoshikawa
kaz@digitallynx.com