The document discusses optional chaining in Swift, demonstrating how to safely access properties and methods of optional values. It provides code examples showing the use of optional chaining to avoid runtime errors when dealing with nil values. Various scenarios are presented, including accessing room counts and addresses, and how to handle multiple levels of optional values.

1. swift 0x12
optional chaining
문현진(arnold@css99.co.kr)
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2. 옵셔널 체인
옵셔널 값이 nil인가요?

3. forced unwrapping
class Person {
var residence: Residence?
}
class Residence {
var numberOfRooms = 1
}
let john = Person()
let roomCount = john.residence.numberOfRooms

4. forced unwrapping
class Person {
var residence: Residence?
}
class Residence {
var numberOfRooms = 1
}
let john = Person()
let roomCount = john.residence.numberOfRooms
Runtime Error

5. forced unwrapping
nil인지 물어본다. (john.residence == nil)
if let roomCount = john.residence?.numberOfRooms {
println("John's residence has (roomCount) room(s).")
} else {
println("Unable to retrieve the number of rooms.")
}
// prints "Unable to retrieve the number of rooms."

6. forced unwrapping
nil인지 물어본다. (john.residence != nil)
john.residence = Residence()
if let roomCount = john.residence?.numberOfRooms {
println("John's residence has (roomCount) room(s).")
} else {
println("Unable to retrieve the number of rooms.")
}
// prints "Unable to retrieve the number of rooms."

7. 옵셔널 체인을 위한 모델 클래스 선언
class Person {
var residence: Residence?
}
class Residence {
var rooms = Room[]()
var numberOfRooms: Int {
return rooms.count
}
subscript(i: Int) -> Room {
return rooms[i]
}
func printNumberOfRooms() {
println("The number of rooms is
(numberOfRooms)")
}
var address: Address?
}

8. 옵셔널 체인을 위한 모델 클래스 선언
class Room {
let name: String
init(name: String) { self.name = name
}
}
class Address {
var buildingName: String?
var buildingNumber: String?
var street: String?
func buildingIdentifier() -> String? {
if buildingName {
return buildingName
} else if buildingNumber {
return buildingNumber
} else {
return nil
}
}
}

9. 옵셔널 체인을 통한 프로퍼티 호출
let john = Person()
if let roomCount = john.residence?.numberOfRooms {
println("John's residence has (roomCount) room(s).")
} else {
println("Unable to retrieve the number of rooms.")
}
// prints "Unable to retrieve the number of rooms."

10. 옵셔널 체인을 통한 메소드 호출
func printNumberOfRooms() {
println("The number of rooms is (numberOfRooms)")
}
if john.residence?.printNumberOfRooms() {
println("It was possible to print the number of rooms.")
} else {
println("It was not possible to print the number of rooms.")
}
// prints "It was not possible to print the number of rooms."

11. 옵셔널 체인을 통한 서브스크립트 호출
if let firstRoomName = john.residence?[0].name {
println("The first room name is (firstRoomName).")
} else {
println("Unable to retrieve the first room name.")
}
// prints "Unable to retrieve the first room name."

12. 옵셔널 체인을 통한 서브스크립트 호출
let johnsHouse = Residence()
johnsHouse.rooms += Room(name: "Living Room")
johnsHouse.rooms += Room(name: "Kitchen")
john.residence = johnsHouse
if let firstRoomName = john.residence?[0].name {
println("The first room name is (firstRoomName).")
} else {
println("Unable to retrieve the first room name.")
}
// prints "The first room name is Living Room."

13. 여러 단계의 체인 연결
if let johnsStreet = john.residence?.address?.street {
println("John's street name is (johnsStreet).")
} else {
println("Unable to retrieve the address.")
}
// prints "Unable to retrieve the address."

14. 여러 단계의 체인 연결
let johnsAddress = Address()
johnsAddress.buildingName = "The Larches"
johnsAddress.street = "Laurel Street"
john.residence!.address = johnsAddress
if let johnsStreet = john.residence?.address?.street {
println("John's street name is (johnsStreet).")
} else {
println("Unable to retrieve the address.")
}
// prints "John's street name is Laurel Street."

15. 옵셔널 반환값을 이용한 메소드 체인
if let buildingIdentifier = john.residence?.address?.buildingIdentifier() {
println("John's building identifier is (buildingIdentifier).")
}
// prints "John's building identifier is The Larches."
if let upper = john.residence?.address?.buildingIdentifier()?.uppercaseString {
println("John's uppercase building identifier is (upper).")
}
// prints "John's uppercase building identifier is THE LARCHES."