This document discusses lessons learned from migrating an application from Objective-C to Swift. It covers various challenges such as interoperability between the two languages, handling optionals and enums, and migrating Objective-C code and patterns to Swift equivalents. Recommendations are provided such as starting the migration with files without subclasses, using Swift features selectively, and adopting a file-by-file migration approach. Potential issues with architectures like MVC and patterns like delegation are also addressed.

1. CASE STUDY: MIGRATING
FROM OBJECTIVE-C TO SWIFT
DOMINIQUE STRANZ

2. MIGRATE
TO SWIFT
STAY WITH
OBJECTIVE-C
?

3. WE DECIDED TO
MIGRATE 🎉

4. CUI BONO?
Lucius Cassius Longinus

5. DEVELOPERS

6. STRING
INTERPOLATION

7. OPTIONALS

8. TUPLES

9. STRING ENUMS

10. NO MORE
HEADER FILES

11. PROTOCOLS
EXTENSIONS

12. and so on,
and so forth…

13. HOW DO
I START?

14. Application
Configuration
Manager
API Client
Utils

15. Application
Configuration
Manager
new API Client
Utils

16. Application
new API Client
Utils
Adopt Nullability
Configuration
Manager

17. Adopt Nullability
Configuration
Manager

18. Adopt Nullability
Configuration
Manager

19. Adopt Nullability
Configuration
Manager

20. Application
new API Client
Utils
Adopt Nullability
Configuration
Manager

21. ALL NEW
FEATURES
WRITTEN
IN SWIFT

22. USE „TECH DAYS”
TO MIGRATE
OBJECTIVE-C
CODE

23. 34%
of code in
after 2 months

24. 53%
of code in
now

25. 3 RULES OF
EFFECTIVE
MIGRATION

26. FILE BY FILE
MIGRATION
IS THE MOST
EFFECTIVE WAYChild2
Base
Child1
Class2
Class4
Class3

27. START WITH
FILES WITHOUT
SUBCLASSES
Child2
Base
Child1
Class2
Class4
Class3
YOU CANNOT SUBCLASS
A SWIFT CLASS IN
OBJECTIVE-C

28. SWIFT CLASS MUST BE
A DESCENDANT OF AN
OBJECTIVE-C CLASS
…TO BE ACCESSIBLE
IN OBJECTIVE-C FILES
Child2
Base
Child1
Class4
Class3
NSObject

29. SWIFT CLASS MUST BE
A DESCENDANT OF AN
OBJECTIVE-C CLASS
Child2
Base
Child1
Class4
Class3
NSObject
OBJECTIVE-C WILL NOT BE
ABLE TO TRANSLATE CERTAIN
SWIFT-SPECIFIC FEATURES

30.
MIXED PROJECTS

31. Mix-and-match functionality makes it easy to choose
which features and functionality to implement in
Swift, and which to leave in Objective-C.
Interoperability makes it possible to integrate those
features back into Objective-C code with no hassle.
Apple Inc. “Using Swift with Cocoa and Objective-C (Swift 3).”

34. BUNDLE SIZE
22 MB 38 MB
YES FOR THE WATCHOS APP
NO FOR THE WATCHOS APP EXTENSION
Always Embed Swift Standard Libraries
⌚

35. CODE AUTOCOMPLETION
FIXED IN XCODE 8.3

36. IMPORTS

37. IN OBJECTIVE-C
HEADER FILES ONLY
USE FORWARD
DECLARATIONS
NSObject
@class ClassName;
@protocol ProtocolName;
IMPORTING A SWIFT HEADER FILE
THERE WILL LEAVE YOU WITH
A CIRCULAR REFERENCE.

38. IF BOTH SWIFT AND
OBJECTIVE-C CLASSES
ARE IN THE SAME
APPLICATION PROJECT
NSObject
#import "ModuleName-Swift.h"

39. IF BOTH SWIFT AND
OBJECTIVE-C CLASSES
ARE IN THE SAME
COCOA POD PROJECT
NSObject
#import <PodName/PodName-Swift.h>

40. IF SWIFT FILE IS
IN ANOTHER POD
NSObject
@import PodName;

41. IF SWIFT FILE IS
IN ANOTHER POD
NSObject
@import PodName;
ADD *.SWIFT FILES TO
SOURCE_FILES DECLARATION
IN PODSPEC FILE

42. SWIFT CLASS
IN OBJECTIVE-C

43. MUST BE A DESCENDANT
OF AN OBJECTIVE-C CLASS
WILL NOT BE VISIBLE
IN OBJECTIVE-C
INT?, INT!, FLOAT?, …
SOME NAMES ARE ALREADY IN
USE IN NSOBJECT
description: String
SWIFT CLASSES CANNOT BE
SUBCLASSED IN OBJECTIVE-C
objc_subclassing_restricted
METHODS WITH NIL
TERMINATION WILL BE NOT
ACCESSIBLE IN SWIFT
NS_REQUIRES_NIL_TERMINATION
DEALLOC IS UNAVAILABLE
IN SWIFT, BUT YOU CAN USE
DEINIT INSTEAD
dealloc != deinit

44. SWIFT ENUM
IN OBJECTIVE-C

45. ENUM SHOULD HAVE THE
@OBJC PREFIX
@objc prefix
ASSOCIATED VALUES
ARE NOT SUPPORTED
case variant1(value: Int)
IN OBJECTIVE-C ENUM CAN
ONLY HAVE INTEGER TYPE
@enum Name: Int

46. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
RawRepresentable enum for ObjectMapper?
▸ Model should provide wrapper for Obj-C code:
▸ Translation to enum: Int
during mapping transformation or in runtime
▸ Computed property `isActive: Bool`, `is…: Bool`

47. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
API Endpoints as URLRequestConvertible enums?
▸ Create a proxy class (inherited from NSObject) with class
requests methods, that inside will use Swift enum
▸ We decided to only define methods really used by Obj-C
More about elegant API Endpoints in Alamofire
https://github.com/Alamofire/Alamofire#crud--authorization

48. WHAT WILL
NSCODER
FAIL TO SEE?

49. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
NSCoding
▸ NSKeyedArchiver, NSKeyedUnarchiver will see only
properties visible for Objective-C
▸ We can change properties type or…

50. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
NSCoding
▸ NSKeyedArchiver, NSKeyedUnarchiver will see only
properties visible for Objective-C
▸ We can change properties type or…
▸ Use value(forUndefinedKey key: String) -> Any? and
setValue(_ value: Any?, forUndefinedKey key: String)
to set/get not bridged properties
▸ Example: Use enum’s rawValue as encodable value

51. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
NSCoding

52. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
Future? Swift Archival & Serialization proposal
▸ It aims to provide a solution for the archival of Swift struct
and enum types
▸ It aims to provide a more type-safe solution for serializing
to external formats, such as JSON and plist
▸ Read more: https://github.com/itaiferber/swift-evolution/
blob/swift-archival-serialization/proposals/XXXX-swift-
archival-serialization.md

53. USING
ENUMERATIONS
AS ERRORS

54. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
enum ServiceError: Error {}

55. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
enum ServiceError: Error {}
▸ Error type in Obj-C code?
NSError without associated values…

56. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
enum ServiceError: Error {}
▸ Error type in Obj-C code?
NSError without associated values…
▸ CustomNSError protocol: Describes an error type that
specifically provides a domain, code, and user-info
dictionary
More: https://github.com/apple/swift-evolution/blob/
master/proposals/0112-nserror-bridging.md

57. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
enum ServiceError: Error {}

58. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
enum ServiceError: Error {}

59. LESSONS
LEARNED

60. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
Optional(„2000 PLN”)

61. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
Optional(„2000 PLN”)
▸ Swift 3.1 will actually actually raise
a warning when you use an optional
in string interpolation
More: https://oleb.net/blog/2016/12/optionals-string-
interpolation

62. CASE STUDY: MIGRATING FROM OBJECTIVE-C TO SWIFT
APNS token == „32bytes”

63. read more at tech.olx.com

64. THANK YOU