This document discusses strategies for migrating code from Swift 2.x to Swift 3.0. It recommends first migrating dependencies using tools like CocoaPods and Carthage. It then recommends using Xcode's migration assistant to fix issues, while also preparing code templates beforehand using tools like SwiftGen. Some challenges discussed include changes made automatically by the migrator, optional comparators being removed, and Grand Central Dispatch API changes. References for further information on the Swift 3 migration are provided.

1. LET’S MIGRATE TO 3.0
COCOAHEADS NANTES
David Bonnet - @iGranDav
19 January 2017

2. A LITTLE BIT OF HISTORY…
▸ From Swift 1.x to Swift 2.x
▸ Just remember ErrorType and throwable types
▸ Swift 3.0 is the first community version !
🎉 "
‣ it also breaks code ! 😅

3. ⚠
STILL NOT ABI STABLE !
Everything needs to be migrated

4. LET’S DO IT SOFTLYSWIFT 2.3

5. LET’S DO IT SOFTLY - SWIFT 2.3
A LIGHTWEIGHT UPDATE
▸ Only takes advantage of Nullability Checking on Objective-C Interoperability
// Swift 2.2
let image = CIImage(MTLTexture: texture, options: options)
let extent = image.extent // this code can lead to a crash
// Swift 3.0
if let image = CIImage(MTLTexture: texture, options: options) {
…
}
▸ This can help you migrate quickly to the SDK 10 on a big base code %
5

6. LET’S DO IT SOFTLY - SWIFT 2.3
A TEMPORARY SOLUTION
▸ Xcode loses code sense (even more than usual)
▸ Sometimes completion code is absent / No code coloration when lost
▸ When showing real-time errors in source code, Xcode can get lost
▸ this is valid swift 2.3 code ! and it builds 🤕
▸ fixed in latest Xcode 8.2.1
▸ Xcode 8.2.x is the last version to support it! 😈
6

7. OK NOW FOR REALSWIFT 3.0

8. APPLE SOLUTION
LET’S MIGRATE - SWIFT 3.0

9. LET’S MIGRATE - SWIFT 3.0
APPLE SOLUTION - MIGRATION ASSISTANT
9

10. LET’S MIGRATE - SWIFT 3.0
APPLE SOLUTION - MIGRATION ASSISTANT IN REAL LIFE
10
😱 Using Xcode 8.0

11. AN APPROACH
LET’S MIGRATE - SWIFT 3.0

12. LET’S MIGRATE - SWIFT 3.0
1. MIGRATE YOUR DEPENDENCIES - COCOAPODS / CARTHAGE
▸ Long live Objective-C! 👻
▸ Almost nothing to do here…
▸ Some authors have annotated their libraries: better swift interoperability!
▸ Others have created a brand new swift version:
▸ MMDrawerController has been converted to DrawerController
drawerController?.openDrawerGestureModeMask = MMOpenDrawerGestureMode.None
[X] ’None' has been renamed to 'none'
12
https://github.com/mutualmobile/MMDrawerController/issues/476
drawerController?.openDrawerGestureModeMask = MMOpenDrawerGestureMode.none
[X] 'none' is unavailable: use [] to construct an empty option set

13. LET’S MIGRATE - SWIFT 3.0
1. MIGRATE YOUR DEPENDENCIES - COCOAPODS / CARTHAGE
▸ ⚠ update your libraries means update also their APIs or introduce new features!
extension Results {
func toArray() -> [T] {
return self.map {$0}
}
}
extension RealmSwift.List {
func toArray() -> [T] {
return self.map {$0}
}
}
13
=>
//New definition in RxRealm
extension List: NotificationEmitter {
public typealias ElementType = Element
public func toArray() -> [Element] {
return Array(self)
}
}

14. 14
▸ Migrate your code template before the migration!
▸ SwiftGen - https://github.com/AliSoftware/SwiftGen
-t swift3
LET’S MIGRATE - SWIFT 3.0
2. USING A CODE GENERATOR?
#!/bin/sh
swiftgen strings

15. 15
▸ Use a linter? Disable it during the migration.
▸ SwiftLint - https://github.com/realm/SwiftLint
1. Launch the migration assistant on your targets only
2. Analyse each source file:
1. Fix it if needed 😅
2. Uncheck from migration when it’s a third party file 😓
3. Do not hesitate to pass the migrator several times
LET’S MIGRATE - SWIFT 3.0
3. SOME OTHER THINGS

16. REAL WORLD PROBLEMSSHARING ISSUES AND FIXING THEM +

17. 17
▸ To avoid renaming all your APIs calls:
▸ _ is automatically added, you probably want to name them properly
func updateIdentityWithName(_ name: String, firstname: String) throws
▸ Some Foundation objects with deleted NS prefix are casted to conform to
new APIs
let url = NSURL(string: "http://someurl.com" )
URLComponents(url: url as URL, resolvingAgainstBaseURL: false)
REAL WORLD PROBLEMS
BEWARE SOME CHANGES ARE MADE AUTOMATICALLY
SE-0046
if let url = URL(string: "http://someurl.com" ) {
URLComponents(url: url, resolvingAgainstBaseURL: false)
}
func updateIdentity(name: String, firstname: String) throws

18. 18
▸ A cast to AnyObject is frequently added although new APIs accept Any
▸ Convert your JSON objects to [String: Any]
▸ ⚠ Some types becomes values types!
▸ public struct Date versus open class NSDate
▸ But it can simplify the reading:
▸ (x as NSDate).earlierDate(y) can be changed to x < y ? x : y
REAL WORLD PROBLEMS
BEWARE SOME CHANGES ARE MADE AUTOMATICALLY
https://developer.apple.com/swift/blog/?id=39

19. 19
▸ Your potential if let or guard let on absoluteString will not be
removed, it’s your job 🙂
▸ Tip: If you absolutely need to keep your code block you can use a do
statement
REAL WORLD PROBLEMS
SOME APIS DO NOT RETURN OPTIONALS ANYMORE
open class NSURL {
open var absoluteString: String? { get }
}
public struct URL {
public var absoluteString: String { get }
}
versus
do {
//your code here
}

20. REAL WORLD PROBLEMS
OPTIONAL COMPARATORS DISAPPEARED
20
// FIXME: comparison operators with optionals were removed from the Swift Standard Libary.
// Consider refactoring the code to use the non-optional operators.
fileprivate func > <T: Comparable>(lhs: T?, rhs: T?) -> Bool {
switch (lhs, rhs) {
case let (l?, r?):
return l > r
default:
return rhs < lhs
}
}

21. 21
▸ Dispatch APIs are not correctly migrated (at least at that time using Xcode 8.0)
DispatchQueue.global(qos: .background).async {
//do some work
}
DispatchQueue.global(qos: .default).asyncAfter(deadline: .now() + 1) {
//do some work in 1s from now
}
▸ dispatch_once doesn’t exist anymore 😢
▸ Use lazily initialised globals or static properties 😎
REAL WORLD PROBLEMS
GRAND CENTRAL DISPATCH
SE-0044 & SE-0088

22. 22
▸ Remember Nullability Checking integrated into Swift 2.3
▸ ImplicitlyUnwrappedOptionals are considered like optionals now, but not
all the time 😅
REAL WORLD PROBLEMS
OBJECTIVE-C INTEROPERABILITY
https://www.natashatherobot.com/swift-3-implicitly-unwrapped-optionals/
because File > New Project is a rare thing
func valueUp(value: Int!) {
// oldValue is an Int?
// since value doesn't need to be type checked
let oldValue = value // Int?
// newValue is an Int,
// since value was forced to unwrap
// b/c it had to be type checked to do the addition
let newValue = value + 1 // Int
[…]
}
valueUp(value: 10)

23. 23
▸ Swift 3 renamed a lot of objective-c based APIs automatically "
▸ Legacy swift annotations are still available
▸ nullability / generics
▸ NS_SWIFT_NAME / NS_REFINED_FOR_SWIFT / NS_SWIFT_UNAVAILABLE
▸ New annotations available
▸ NS_NOESCAPE to annotate your objective-c blocks (eg. @noespace)
▸ NSEXTENSIBLESTRING_ENUM to convert a string based obj-c enum to a struct
REAL WORLD PROBLEMS
OBJECTIVE-C INTEROPERABILITY
https://realm.io/news/altconf-nikita-lutsenko-objc-swift-interoperability/
because File > New Project is a rare thing

24. 24
▸ I had to convert manually CGFloat.max to CGFloat.greatestFiniteMagnetude
▸ OptionSet are not converted as expected for default values :
▸ UIControlState() instead of .normal : it works but less readable
▸ Visibility changes : private becomes fileprivate etc…
▸ ⚠ Be aware of open versus public on your libraries
REAL WORLD PROBLEMS
SOME RANDOM NOTES
SE-0067

25. 25
▸ map or flatmap returns LazyCollection types now :
▸ let list = Array(myLazyCollection) if you really need a Collection
▸ New compiler : new warnings like unused results 👾
▸ You can add _ to discard it: _ = foo()
▸ returned result is secondary: @discardableResult on the function can
also avoid this warning
REAL WORLD PROBLEMS
SOME RANDOM NOTES
SE-0067

26. QUESTION TIMETHANKS FOR YOUR ATTENTION 😀

27. 27
▸ A (mostly) comprehensive list of Swift 3.0 and 2.3 changes
▸ https://buildingvts.com/a-mostly-comprehensive-list-of-swift-3-0-and-2-3-changes-193b904bb5b1
▸ Swift migration guide
▸ https://swift.org/migration-guide/
▸ WWDC 2016 - Session 402 : What’s new in swift
▸ https://developer.apple.com/videos/play/wwdc2016/402/
▸ AltConf - Advanced ObjC <-> Swift Interoperability
▸ https://realm.io/news/altconf-nikita-lutsenko-objc-swift-interoperability/
LET’S MIGRATE TO 3.0
REFERENCES
David Bonnet - @iGranDav
david.bonnet@cocoaheads.fr