Swift 3 Programming for iOS : extension

Swift 3 :
Extensions
군산대학교 컴퓨터정보통신공학부 컴퓨터정보공학전공
남 광 우
kwnam@kunsan.ac.kr
Swift 3 Tour and Language Guide by Apple

Extension
• 정의
• 이미 존재하는 클래스나 구조체, 열거형 등의 객체에
새로운 기능을 확장
• 사용 목적
• Add computed instance properties / computed type properties
• Define instance methods and type methods
• Provide new initializers
• Define subscripts
• Define and use new nested types
• Make an existing type conform to a protocol
Extension 확장할 객체 {
// enumeration definition goes here
}

Extension
• 확장 구문의 정의
• Extension의 예
Extension 확장할 객체 {
// enumeration definition goes here
}
extension SomeType: SomeProtocol, AnotherProtocol {
// implementation of protocol requirements goes here
}
extension Double {
var km: Double { return self * 1_000.0 }
var m: Double { return self }
var cm: Double { return self / 100.0 }
var mm: Double { return self / 1_000.0 }
var ft: Double { return self / 3.28084 }
}

• Extension의 사용 예
• Extension의 연산 예
let oneInch = 25.4.mm
print("One inch is (oneInch) meters")
// Prints "One inch is 0.0254 meters“
let threeFeet = 3.ft
print("Three feet is (threeFeet) meters")
// Prints "Three feet is 0.914399970739201 meters"
let aMarathon = 42.km + 195.m
print("A marathon is (aMarathon) meters long")
// Prints "A marathon is 42195.0 meters long"
extension Double {
var km: Double { return self * 1_000.0 }
var m: Double { return self }
var cm: Double { return self / 100.0 }
var mm: Double { return self / 1_000.0 }
var ft: Double { return self / 3.28084 }
}
Extension

Extension : Initializer
• Initializer의 확장
• Before extension
struct Size {
var width = 0.0, height = 0.0
}
struct Point {
var x = 0.0, y = 0.0
}
struct Rect {
var origin = Point()
var size = Size()
}
let defaultRect = Rect()
let memberwiseRect =
Rect(origin: Point(x: 2.0, y: 2.0), size: Size(width: 5.0, height: 5.0))

Extension : Initializer
• Initializer의 확장
• After init extension
extension Rect {
init(center: Point, size: Size) {
let originX = center.x - (size.width / 2)
let originY = center.y - (size.height / 2)
self.init(origin: Point(x: originX, y: originY), size: size)
}
}
let centerRect = Rect(center: Point(x: 4.0, y: 4.0),
size: Size(width: 3.0, height: 3.0))
// centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0)

Extension : Method
• Method의 확장 예
• 사용 예
extension Int {
func repetitions (task: () -> Void) {
for _ in 0..<self {
task()
}
}
}
3.repetitions {
print("Hello!")
}
// Hello!
// Hello!
// Hello!

Extension : Method
• Mutating Method의 확장 예
• 사용 예
extension Int {
mutating func square() {
self = self * self
}
}
var someInt = 3
someInt.square()
// someInt is now 9

extension Int {
subscript(digitIndex: Int) -> Int {
var decimalBase = 1
for _ in 0..<digitIndex {
decimalBase *= 10
}
return (self / decimalBase) % 10
}
}
Extension : Subscript
• Subscript의 확장 예
• 사용 예
746381295[0]
// returns 5
746381295[1]
// returns 9
746381295[2]
// returns 2
746381295[8]
// returns 7

Extension : nested type
• Nested type의 확장 예
extension Int {
enum Kind {
case negative, zero, positive
}
var kind: Kind {
switch self {
case 0:
return .zero
case let x where x > 0:
return .positive
default:
return .negative
}
}
}

Extension : nested type
• Nested type의 사용 예
func printIntegerKinds(_ numbers: [Int]) {
for number in numbers {
switch number.kind {
case .negative:
print("- ", terminator: "")
case .zero:
print("0 ", terminator: "")
case .positive:
print("+ ", terminator: "")
}
}
print("")
}
printIntegerKinds([3, 19, -27, 0, -6, 0, 7])
// Prints "+ + - 0 - 0 + "

Swift 3 Programming for iOS : extension

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