Idioms in swift 2016 05c

Idioms in Swift
Kaz Yoshikawa
May 2016

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.

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
}

if let
• if let を使う
if let a = a, let b = b {
return a + b
}
return nil
}

where
• guard let で０以上を保証する
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
if let a = a, let b = b where a >= 0 && b >= 0 {
return a + b
}
return nil
}

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)
}

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
}
}

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

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")
}
}

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)")
}

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)")
}
}

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])

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")
}

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)")
}

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
}

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!!
}
}
}

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()
}

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()
}
}() // "()" !!

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
}
}

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

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)
}()
}

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
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

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

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

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)")
}

for var i = 99 ; i >= 0 ; i--
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)")
}

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

for var i = 98 ; i >= 0 ; i -=
2
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)")
}

for without increment
• 次の再初期化式の指定がなく、刻みが不定の場合
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 }
}

Computed Properties
and Property Observer

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

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

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

Thank You
Kaz Yoshikawa
kaz@digitallynx.com

Idioms in swift 2016 05c

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