Written by Amy
on September 19, 2017

스위프트 Enum

Swift Terminology - Enumeration

Sources from The Swift Programming Language (Swift 4), Appventure.me

An enumeration defines a common type for a group of related values and enables you to work with those values in a type-safe way within your code.

필요한 상황

유한한 경우의 수가 있을 때, 케이스(+때로는 연관된 값)를 선언하는 것
Define any hierarchically organized data
Keeping related information together.

기본 문법

enum CompassPoint {
    case north
    case south
    case east
    case west
}

var directionToHead = CompassPoint.west
directionToHead = .north

스위치문과 함께 사용하기

Enum을 활용하는 패턴 매칭
You can use various pattern matching constructs through enums

directionToHead = .south
switch directionToHead {
case .north:
    print("Lots of planets have a north")
case .south:
    print("Watch out for penguins")
case .east:
    print("Where the sun rises")
case .west:
    print("Where the skies are blue")
}
// Prints "Watch out for penguins"

값 할당하기 (Associated Values)

01. 값을 할당하는 “바코드” 열거형 만들기

enum Barcode {
    case upc(Int, Int, Int, Int) // 이건 어찌보면 튜플이 할당된 케이스!
    case qrCode(String)
}

02. 바코드의 인스턴스 만들기

var productBarcode: Barcode = Barcode.upc(1, 2, 3, 4)
productBarcode = .qrCode("BONJOUR")

03. 스위치문 사용하기

👋🏻 스위프트 구문 안에서 값 바인딩 시키기

switch productBarcode {
    case .upc(let numberSystem, let manufacturer, let product, let check):
    print("UPC: \(numberSystem), \(manufacturer), \(product), \(check).")
    case .qrCode(let productCode):
    print("QR CODE: \(productCode).")
}

👋🏻 와일드카드를 사용할 수도 있다.

switch bookBarcode {
    case .upc(let numberSystem, _, _, _) where numberSystem == 8:
        print("This is imported Journals.")
    case .qrCode(let productCode):
        print("QR CODE: \(productCode).")
	default:
    print("default")
}

04. 예제: 바코드 첫번째 숫자로 책 타입을 구분해보기

enum Barcode {
    case upc(Int, Int, Int, Int)
    case qrCode(String)
}

var kinfolk: Barcode = Barcode.upc(8, 2, 3, 4)
var photography: Barcode = Barcode.upc(111, 2, 3, 4)
var foody: Barcode = Barcode.upc(11, 2, 3, 4)

func checkBookType(bar: Barcode) {
    switch bar {
    case .upc(let bookType, _, _, _) where bookType < 10 && 0 < bookType:
        print("This is a journal.")
    case .upc(let bookType, _, _, _) where bookType >= 10 && 20 > bookType:
        print("This is a cook Book.")
    case .upc(let bookType, _, _, _) where bookType >= 20 && 500 > bookType:
        print("This is a photography book.")
    default:
        print("Anything else")
    }
}

checkBookType(bar: kinfolk)
checkBookType(bar: photography)
checkBookType(bar: foody)

Enum Values: Raw Value

enum 선언시 타입을 Character, Int, String 으로 지정하고 원시값 지정이 가능하다.
Enumeration cases can come prepopulated with default values (called raw values), which are all of the same type.

Mapping to String

enum House: String {
    case Baratheon = "Ours is the Fury"
    case Greyjoy = "We Do Not Sow"
    case Martell = "Unbowed, Unbent, Unbroken"
    case Stark = "Winter is Coming"
    case Tully = "Family, Duty, Honor"
    case Tyrell = "Growing Strong"
}

Mapping to Integer, 디폴트는 0부터 ~

enum Planet: Int {
    case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
} // mercury = 0

let possiblePlanet:Planet = Planet(rawValue: 1)! // venus
print(possiblePlanet.rawValue) // 1

Mapping to Integer, 시작값 지정 가능

enum Planet: Int {
    case mercury=3, venus, earth, mars, jupiter, saturn, uranus, neptune
} // mercury = 3

let possiblePlanet:Planet = Planet(rawValue: 1)! // venus
print(possiblePlanet.rawValue) // 1

Mapping to floating point

also note the fancy unicode in enum cases

enum Constants: Double {
    case π = 3.14159
    case e = 2.71828
    case φ = 1.61803398874
    case λ = 1.30357
}

Properties

실제적인 stored properties 를 저장할 수 없다고 하더라도, computed properties를 활용해볼 수 있다.

enum Device {
  case iPad, iPhone
  var year: Int {
    switch self {
	case iPhone: return 2007 // enum의 케이스 하위에 year 생성됨
	case iPad: return 2010
     }
  }
}

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