enumeration

Enumerations - The Swift Programming Language (Swift 5.6)
defines a common type for a group of related values and enables you to work with those values in a type-safe way
◇相関値のバインド時に→type-safe

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")
}

iterating over enum case
←:CaseIterableプロトコル、CASEに繰り返しアクセス可能

enum Beverage: CaseIterable {
    case coffee, tea, juice
}

let numberOfChoices = Beverage.allCases.count
print("\(numberOfChoices) beverages available")
// Prints "3 beverages available"

for beverage in Beverage.allCases {
    print(beverage)
}
// coffee
// tea
// juice

Associated Values

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

var productBarcode = Barcode.upc(8, 85909, 51226, 3)
productBarcode = .qrCode("ABCDEFGHIJKLMNOP")

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).")
}
// Prints "QR code: ABCDEFGHIJKLMNOP."

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

Implicitly assigned raw values

enum Planet: Int {
    case mercury = 1, venus, earth, mars, jupiter, saturn, uranus, neptune
}

let earthsOrder = Planet.earth.rawValue
// earthsOrder is 3

enum CompassPoint: String {
    case north, south, east, west
}

let sunsetDirection = CompassPoint.west.rawValue
// sunsetDirection is "west"

If you define an enumeration with a raw-value type, the enumeration automatically receives an initializer that takes a value of the raw value’s type (as a parameter called  rawValue ) and returns either an enumeration case or  nil .
=initとrawValueを使用してenumを作成するには、傍観者→対応するcaseを返すか、nilがない場合

let positionToFind = 11
if let somePlanet = Planet(rawValue: positionToFind) {
    switch somePlanet {
    case .earth:
        print("Mostly harmless")
    default:
        print("Not a safe place for humans")
    }
} else {
    print("There isn't a planet at position \(positionToFind)")
}
// Prints "There isn't a planet at position 11"