Condensed version presented at MBLT:Dev 2016 in Moscow. NOTE: Created in Keynote, exported to PowerPoint, so maybe some slight issues

1. Keith Moon - Senior iOS Developer
Thinking In Swift
MBLT.dev - Moscow
November 2016

2. 2
• iOS Developer since 2010
• Worked with BBC News, Hotels.com and Travelex
• Working in Swift since it’s release
• Built 2 apps end to end in Swift
• “Swift 3 Cookbook” to be published by Pakt
Who am I?
@keefmoon

3. 3
• Help users discover great local food
• Make it quick and easy to order from a wide variety of takeaways
• Available on:
–Web
–iOS
–Android
–Amazon Echo
What is Just Eat?
3

4. 4
• Australia
• Brazil
• Canada
• Denmark
• France
• Ireland
• Italy
• Mexico
What is Just Eat?
Global Business
• New Zealand
• Norway
• Spain
• Switzerland
• UK

5. 5
• 12 iOS Developers
• Organised around feature teams
• Mixture of Objective-C and Swift
• Regular releases
• Multi-Variant Testing
• Research team investigating new technology
What is Just Eat?
5

6. 6
What is Just Eat?
• 12 iOS Developers
• Organised around feature teams
• Mixture of Objective-C and Swift
• Regular releases
• Multi-Variant Testing
• Research team investigating new technology

7. 7
Purpose of this talk?
• Swift is fundamentally different to Objective-C
• Not just different syntax
• Swift has more “tools in the toolbox”
How do we “think in Swift”?

8. How do we “think in Swift”?
8
• Use constructs that more closely match the model
• Write code that is hard to use wrong
• Remove the need for trivial tests
• Consider a Protocol orientated approach

9. Structs
The right tool for the job
Class Objects
Enums
Protocols
+ Extensions
Constrained
Extensions
Tuples

10. Enums
• Integer based
• Typedef
• …and that’s it.
typedef enum : NSUInteger {
JEPaymentOptionCash,
JEPaymentOptionSavedCard,
JEPaymentOptionApplePay,
JEPaymentOptionAccountCredit
} JEPaymentOption;
- (void)payByOption:(JEPaymentOption)option {
// Pay ...
}

11. Enums
• Based on any RawRepresentable
enum PaymentOption: String {
case cash
case savedCard
case applePay
case accountCredit
}

12. Enums
• Based on any RawRepresentable
• … or not.
enum PaymentOption {
case cash
case savedCard
case applePay
case accountCredit
}

13. Enums
• Based on any RawRepresentable
• … or not.
• Associated Types
enum PaymentOption {
case cash
case savedCard(SavedCard)
case applePay
case accountCredit
}

14. Enums
• Based on any RawRepresentable
• … or not.
• Associated Types
• Methods
enum PaymentOption {
case cash
case savedCard(SavedCard)
case applePay
case accountCredit
func canPay(at rest: Restaurant) -> Bool {
//...
}
}

15. Enums
• Based on any RawRepresentable
• … or not.
• Associated Types
• Methods
• Computed variables
enum PaymentOption {
case cash
case savedCard(SavedCard)
case applePay
case accountCredit
func canPay(at rest: Restaurant) -> Bool {
//...
}
var isDeviceSupported: Bool {
//...
}
}

16. Example App
16

17. Value Type Semantics
17
SearchFilter
postcode: BR13HP
cuisine: nil
S

18. Value Type Semantics
18
SearchFilter
postcode: BR13HP
cuisine: nil
S
SearchFilter
postcode: BR13HP
cuisine: nil
S

19. Value Type Semantics
19
SearchFilter
postcode: BR13HP
cuisine: nil
S
SearchFilter
postcode: BR13HP
cuisine: Chicken
S

20. Value Type Semantics
20
SearchFilter
postcode: BR13HP
cuisine: nil
S

21. Reference Type Semantics
21
SearchFilter
postcode: BR13HP
cuisine: nil
C

22. Reference Type Semantics
22
SearchFilter
postcode: BR13HP
cuisine: nil
C

23. Reference Type Semantics
23
SearchFilter
postcode: BR13HP
cuisine: Chicken
C

24. Reference Type Semantics
24
SearchFilter
postcode: BR13HP
cuisine: Chicken
C

25. enum Cuisine: Int {
case american
case bangladeshi
//...
case thai
case turkish
init?(string: String) {
guard let index = Cuisine.stringValues.index(of: string),
let cuisine = Cuisine(rawValue: index) else {
return nil
}
self = cuisine
}
var displayString: String {
return Cuisine.stringValues[rawValue]
}
private static var stringValues: [String] {
return ["American",
"Bangladeshi",
//...
"Thai",
"Turkish"]
}
}
25
enum Cuisine: Int, CaseCountable {
case american
case bangladeshi
//...
case thai
case turkish
init?(string: String) {
for index in 0..<Cuisine.caseCount {
if let cuisine = Cuisine(rawValue: index),
cuisine.displayString == string {
self = cuisine
return
}
}
return nil
}
var displayString: String {
return String(describing: self).capitalized
}
}
Cuisine Enum -
NewOld

26. restaurantService.fetchRestaurants(for: postcode) { [weak self] (fetchedRestaurants, error) in
if let fetchedRestaurants = fetchedRestaurants {
self?.allRestaurants = fetchedRestaurants
self?.visibleRestaurants = fetchedRestaurants
self?.tableView.reloadData()
} else if let error = error {
// Handle Error
print(error)
}
}
26
enum RestaurantResult {
case success([Restaurant])
case failure(Error)
}
restaurantService.fetchRestaurants(for: postcode) { [weak self] result
in
switch result {
case .success(let fetchedRestaurants):
self?.allRestaurants = fetchedRestaurants
self?.visibleRestaurants = fetchedRestaurants
self?.tableView.reloadData()
case .failure(let error):
// Handle Error
print(error)
}
}
Networking Result -
New
Old

27. Reference Type Semantics
27
Margherita Pizza
C
Vegetarian Pizza
C
Coca-Cola
C
Sprite
C

28. Reference Type Semantics
28
Margherita Pizza
C
Vegetarian Pizza
C
Coca-Cola
C
Sprite
C

29. Reference Type Semantics
29
Margherita Pizza
C
Vegetarian Pizza
C
Coca-Cola
C
Sprite
C

30. Value Type Semantics
30
Margherita Pizza
S
Vegetarian Pizza
S
Vegetarian Pizza
S
Coca-Cola
S
Coca-Cola
S
Sprite
S

31. Value Type Semantics
31
Margherita Pizza
S
Vegetarian Pizza
S
Vegetarian Pizza
S
Coca-Cola
S
Coca-Cola
S
Sprite
S

32. Value Type Semantics
32
Margherita Pizza
S
Vegetarian Pizza
S
Vegetarian Pizza
S
Coca-Cola
S
Coca-Cola
S
Sprite
S

33. Summary
● Pick the appropriate Swift type for the concept being modelled
● Consider the Type semantics
● Defining behaviours as protocols can produce expressive code
● Avoid “Stringly” typed implementations
● Try to anticipate and prevent future developer errors
33

34. Thanks! @keefmoon
keith.moon@just-eat.com
keefmoon