This document discusses functions and closures in Swift. It provides examples of defining functions, passing functions as arguments, returning functions from other functions, capturing values from outer scopes within closures, and using lazy initialization to avoid strong reference cycles and memory leaks. Specifically: 1. It shows functions taking other functions as arguments and returning functions. 2. It demonstrates using closures to define functions inline and passing them to other functions. 3. It provides an example of capturing external values within closures and how to avoid strong reference cycles when doing so. 4. It explains how to use lazy initialization with the @lazy property wrapper to lazily initialize properties and avoid memory leaks.

1. SWIFT
2014.7.9
bOb_sTrane@Phybbit
/ /twitter github Qiita

2. Swift
Swift

3. @bOb_sTrane(Qiita/Twitter)
Phybbit iOS /Rails
( ...) , FRP
(Lisp Scala Haskell )

4. SWIFT

5. SWIFT
1.
2.
3.
4.

6. // Intの引数2つを取り、和を返す関数
func add(a: Int, b: Int) -> Int{
return a + b
}
// Intの引数2つを取りIntを返す関数型を引数する関数
func someFunc(mathFunction: (Int, Int) -> Int, a: Int, b: Int) {
println(mathFunction(a, b))
}
someFunc(add, 100, 200) // 300が出力

7. func stepForward(input: Int) -> Int {
return input + 1
}
func stepBackward(input: Int) -> Int {
return input - 1
}
func chooseStepFunction(isBackward: Bool) -> (Int) -> Int {
return isBackward ? stepBackward : stepForward
}
var currVal = 10
let moveNearerToZero = chooseStepFunction(currVal > 0)
while currVal != 0 {
currVal = moveNearerToZero(currVal)
println(currVal) // 0まで1ずつカウントダウン
}

8. // 普通に定義
func greeting(name: String) {
println("Hello (name)")
}
greeting("Taro")
// 関数を変数に代入して定義
let greeting = { (name:String) -> Void in
println("Hello (name)")
}
greeting("Taro")

9. func chooseStepFunction(isBackward: Bool) -> (Int) -> Int {
// 関数内で関数を宣言
func stepForward(input: Int) -> Int { return input + 1 }
func stepBackward(input:Int) -> Int { return input - 1 }
return isBackward ? stepBackward : stepForward
}
var currentValue = -4
let moveNearerToZero = chooseStepFunction(currentValue > 0)
while currentValue != 0 {
currentValue = moveNearerToZero(currentValue)
println(currentValue)
}
// while currentValue != 0 {
// stepForwardがスコープ外のため実行できない
// currentValue = stepForward(currentValue)
// }

10. let names = ["Taro", "Jiro", "Saburo", "Shiro", "Goro"]
// 通常の定義方法
sorted(names) {(s1:String, s2:String) -> Bool in return s1 > s2 }
// [Taro, Shiro, Saburo, Jiro, Goro]
// 型推論 (sorted関数の定義から推論される)
sorted(names) { s1, s2 in return s1 > s2}
// 引数名の自動生成 & 暗示的なreturn
sorted(names) { $0 > $1 }

11. (Blocks )
class LeakPerson {
var name: String
@lazy var greeting: String = { return "Hello, (self.name)" }()
init(name: String) { self.name = name }
deinit { println("LeakPerson deinit called") }
}
var leakPerson: LeakPerson! = LeakPerson(name:"Leak")
println(leakPerson.greeting)
leakPerson = nil // deinitがコールされない

12. class Person {
var name: String
@lazy var greeting: String = { [unowned self] in return "Hello, (self.name)" }()
init(name: String) { self.name = name }
deinit { println("Person deinit called") }
}
var person: Person! = Person(name:"NotLeak")
println(person.greeting)
person = nil // deinitがコールされる

13. SWIFT

14. SWIFT
@lazy

15. class Person {
var name: String
@lazy var personalizedGreeting: String = {
[unowned self] in
println("heavy task started")
// Something very heavy task
for value in 0...20000000 {
if value > 10000000 && value % 100000 == 0{
println("value is (value)")
}
}
println("personalizedGreeting called")
return "Hello, (self.name)!"
}()

16. ( )
init (name:String) {
self.name = name
println("initialized")
}
deinit {
println("destructed")
}
}
var person: Person! = Person(name: "Strange Bob")
println("person object has initialized")
println(person.personalizedGreeting)
person = nil
personalizedGreeting

17. Blocks
lazy

18. Swift
Swift --
Swift @lazy
How to do proper LazyLoadingin Swift
Learn SwiftbyrunningScripts
MemoryLeaks In The SwiftPlayground
LazyInitialization with Swift

20. 7 1 otakyou.com
( )https://www.otakyou.com/