This document discusses optionals in Swift, which represent values that may or may not be present. It begins by providing usage examples of optionals and explaining that they can represent the absence of a value. It then discusses how optionals are implemented behind the scenes using enums, generics, and extensions. The document also covers different techniques for unwrapping optionals safely and unsafely as well as ways to declare, map, and transform optionals. It concludes by presenting some useful optional extensions.

1. Let’s talk about
Optionals
Swift Paris Junior at

2. 1. Introduction 📌
What are optionals?

3. Usage Example
let users: [Int: String] =
[1: "Johny", 2: "Bernard", 3: "Lucie"]
let user1 = users[1]
let user5 = users[5]
User with id 1?
User with id 5?

4. Usage Example
let users: [Int: String] =
[1: "Johny", 2: "Bernard", 3: "Lucie"]
let user1 = users[1]
let user5 = users[5]
Optionals = represents either a wrapped value or
the absence of a value

5. User with id 1?
User with id 5?
let users: [Int: String] =
[1: "Johny", 2: "Bernard", 3: "Lucie"]
let user1 = users[1]
let user5 = users[5]
//Optional(« Johny")
Usage Example

6. User with id 1?
User with id 5?
let users: [Int: String] =
[1: "Johny", 2: "Bernard", 3: "Lucie"]
let user1 = users[1]
let user5 = users[5]
//Optional(« Johny")
//nil
Usage Example

7. Declare Optionals
Notation ?
var name: String?
var firstName: String? = "Sonia"
let age: Int? = 12
name = "Dupont"
firstName = nil

8. var name: String? init(name: String,
firstName: String,
nickname: String?)
func getDateFrom(month: Int,
year: Int) -> Date?
Variables Function’s params
Function’s return types
Declare Optionals

9. 2. Implementation 🛠
What’s behind optional?

10. Wrapper
public enum Optional<Wrapped> {
case none
case some(Wrapped)
}
❌
📦

11. Generics
public enum Optional<Wrapped> {
case none
case some(Wrapped)
}
Compatible with primitives and customs types.

12. Extensions
extension Optional: Equatable where Wrapped: Equatable {
// ...
}
Equatable : Comparison between optional values
Where : Conditional conformance
Wrapped types need to implement Equatable

13. Naive approach
let name: String? = "Valentine"
let name = Optional.some("Valentine")
let firstName: String?
let firstName = Optional.none
Declaration

14. Naive approach
func sayHello(to firstName: Optional<String>) {
switch firstName {
case .some(let value):
print("Hello (value)")
case .none:
print("Hello you")
}
}
Access optional

15. 3. Unwrapping 🎁
« See what’s inside »

16. Safe ✅ Unsafe ✴
Unwrapping techniques
Optional bindings, nil coalescing,
optional chaining…
Force unwrapping, implicitly
unwrapped…

17. Safe techniques ✅
func sayHello(to name: String?) {
if let name = name {
print("Hello (name)")
} else {
print("Hello you")
}
}
if let

18. Safe techniques ✅
func sayHello(to name: String?) {
guard let name = name else {
return
}
print("Hello (name)")
}
guard let

19. Safe techniques ✅
func sayHello(to name: String?) {
guard let name = name else {
return
}
print("Hello (name)")
}
guard let

20. Safe techniques ✅
func sayHello(to name: String?) {
let helloSuffix = name ?? "you"
print("Hello " + helloSuffix)
}
nil coalescing

21. Safe techniques ✅
func sayHello(to name: String?) {
if let name = name {
print("Hello (name)")
} else {
print("Hello you")
}
}
func sayHello(to name: String?) {
guard let name = name else {
return
}
print("Hello (name)")
}
if let guard let
nil coalescing
func sayHello(to name: String?) {
let helloSuffix = name ?? "you"
print("Hello " + helloSuffix)
}

22. Unsafe techniques ✴
func sayHello(to name: String?) {
print("Hello (name!)")
}
force unwrapping

23. Unsafe techniques ✴
func sayHello(to name: String?) {
print("Hello (name!)")
}
@IBOutlet var usernameTextField: UITextField!
force unwrapping
implicit unwrapping

24. Safe 👍 Unsafe ☠
Safe vs Unsafe
In theory better in any case!
Limit as much as possible
Some exceptions: Inform compilator,
debug tool…

25. 4. Create Optionals 🖌
Where else are optionals ?

26. Optional typecast
if let cell = collectionView.dequeueReusableCell(for:
indexPath) as? CZGalleryAlbumViewCell {}
as?

27. Optional try
guard let jsonData = try? Data(contentsOf:
URL(fileURLWithPath: path))
else {
throw RuntimeError("jsonData failed")
}
try?

28. Failable initializer
init?(_ description: String)
let one = Int("1")
let two = Int("two")
init?

29. Failable initializer
init?(_ description: String)
let one = Int("1")
let two = Int("two")
init?
//Optional(1)
//nil

30. Find the type 🎯
Let’s play together!

31. Example 1
protocol User {}
struct Admin: User {}
let user: User? = Admin()
let admin = user as? Admin
Type of admin ? Admin? or Admin??

32. Example 1
protocol User {}
struct Admin: User {}
let user: User? = Admin()
let admin = user as? Admin //Admin?
Type of admin ? Admin? or Admin??

33. Example 2
enum AccessType {
case read
case write
}
struct Admin {
func grantAccess(to: AccessType)
throws -> [AccessType] {
//...
}
}
let admin: Admin? = Admin()
let adminAccess = try? admin?.grantAccess(to: .read)
Type of adminAccess ? [AccessType]? or [AccessType]??

34. Example 2
enum AccessType {
case read
case write
}
struct Admin {
func grantAccess(to: AccessType)
throws -> [AccessType] {
//...
}
}
let admin: Admin? = Admin()
let adminAccess = try? admin?.grantAccess(to: .read) //[AccessType]??
Swift 4 and less
Type of adminAccess ? [AccessType]? or [AccessType]??

35. Example 2
enum AccessType {
case read
case write
}
struct Admin {
func grantAccess(to: AccessType)
throws -> [AccessType] {
//...
}
}
let admin: Admin? = Admin()
let adminAccess = try? admin?.grantAccess(to: .read)
Swift 5
Type of adminAccess ? [AccessType]? or [AccessType]??
//[AccessType]?

36. Example 3
let users: [String: Int?] = ["theo@gmail.com": 21,
"lucille@gmail.com": 45,
"charles@laposte.net" : nil]
let theoAge = users["theo@gmail.com"]
Type of theoAge ? Int? or Int??

37. Example 3
let users: [String: Int?] = ["theo@gmail.com": 21,
"lucille@gmail.com": 45,
"charles@laposte.net" : nil]
let theoAge = users["theo@gmail.com"] //Int??
Type of theoAge ? Int? or Int??

38. 5. Transform Optionals 🔮

39. Map
🧪📤 📥
Unwrap Tranform Wrap
1 2 3

40. Map
let number: Int? = 10
let square = number.map { $0 * $0 } //Int?

41. Map
let number: String? = "10"
1. Transform String into Int
2. Square transformation

42. Map
let number: String? = "10"
let square = number.map { Int($0) }

43. Map
let number: String? = "10"
let square = number.map { Int($0) }
Unwrap Tranform Wrap
1 2 3
Optional("10")
"10" Optional(10) Optional(
Optional(10))
//Int??

44. Map
let number: String? = "10"
let square = number.map { Int($0) }?.map { $0 * $0 }

45. Use flatmap
let number: String? = "10"
let square = number.flatMap { Int($0) }.map { $0 * $0 }

46. FlatMap
🧪📤 📥
Unwrap Tranform Wrap
1 2 3

47. Map or FlatMap ?
Transform
closure
Optionals?
Yes
No
Map
FlatMap

48. Bonus - Extensions 🔥
Pimp your optionals!

49. Examples
extension Optional {
func notNil() -> Bool {
return self != nil
}
func or(_ defaultValue: Wrapped) -> Wrapped {
return self ?? defaultValue
}
func filter(_ predicate: (Wrapped) -> Bool) -> Wrapped? {
guard let unwrapped = self,
predicate(unwrapped) else { return nil }
return self
}
}

50. Examples
var score: Int?
let displayedScore = score ?? 0
let displayedScore = score.or(0)

51. Examples
if let score = score, score > 10 {
print("you win")
} else {
print("you lose")
}

52. Examples
if let score = score, score > 10 {
print("you win")
} else {
print("you lose")
}
print(score.filter({ $0 > 10 }).notNil()
? "you win" : "you lose")

53. Thanks!
Optional Questions?

54. Sources
• The Complete Guide to Optionals in Swift - Paul Hudson
• Optionals in Swift explained: 5 things you should know - Antoine Van Der Lee
• Swift! Optionals? - Sebastian Boldt
• Optionals in Swift: The ultimate guide - Reinder de Vries
• Swift 5.0 is changing optional try - Paul Hudson
• Useful Optional Extensions - Benedikt Terhechte