This document discusses migrating from Objective-C to Swift and some of the benefits and challenges of doing so. It notes that Swift will provide gains like types, generics, and simplicity while some Objective-C features like .h/.m files will be lost. It provides recommendations for how to start migrating an existing Objective-C project to Swift like adding imports to a bridging header and optimizing Objective-C for Swift. Specific examples are given of how Swift can make code easier to read and maintain.

1. func migrating(from: ObjC) -> Swift!
[objC autorelease]

2. Why?

3. https://twitter.com/clattner_llvm

4. WWDC Appearances
swift objective-c
2014
19 63
2015
71 15

5. „…in future, all the
nice things will only
come to swift…“
Apple Software Engineer

6. What will you lose
on the way?

7. * [ ] .h .m
Good old Friends

8. Runtime Dynamics
NSInvocation
NSMethodSignature
[obj load]
nil messaging
Macros
https://developer.apple.com/swift/blog/?id=19

9. What will you gain?

10. Types
Autoclosures
Structs
Generics
Implicit Member Expressions
Custom Operators
Typealiases
Enums
Currying
Recursive Enumerations
Property ObserversProtocol Extensions
Generators
Subscripts
Optionals
Lazyness
Pattern Matching
Tuples
Immutability
ErrorType
Access Control

11. Simplicity
view.backgroundColor = .redColor()
[view setBackgroundColor: [UIColor redColor]]

12. @warn_unused_result func flatMap<T>
(@noescape _ transform:
(Self.Generator.Element) throws -> T?)
rethrows -> [T]
Kinda Simplicity
https://developer.apple.com/library/ios/documentation/Swift/Reference/
Swift_SequenceType_Protocol/index.html

13. https://github.com/typelift/Swiftz/blob/master/Swiftz/EitherExt.swift
Not-So-Simplicity-At-All

14. What will remain?

15. SDK
XYZKit
Model View Controller
Retain Cycles
Xcode

16. How to start?

17. Existing Objective-C Project
No Warnings 😇
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/
BuildingCocoaApps/index.html#//apple_ref/doc/uid/TP40014216-CH2-ID0
Using Swift with Cocoa and Objective-C

18. Bridging Header
Add Imports as you need them
Automatically generated by compiler
Generated Header
…using obj-c in swift…
…using swift in obj-c…

19. Optimize Obj-C for Swift
NS_ASSUME_NONNULL_BEGIN
nonnull|nullable|null_unspecified
NSArray<__kindof UIView *> *someViews;
https://developer.apple.com/videos/play/wwdc2015-401/

20. Try to avoid designing
Swift for Obj-C
You’ll have access to anything within a class or protocol that’s
marked with the @objc attribute as long as it’s compatible with Objective-C.
This excludes Swift-only features such as those listed here:
Generics
Tuples
Enumerations defined in Swift without Int raw value type
Structures defined in Swift
Top-level functions defined in Swift
Global variables defined in Swift
Typealiases defined in Swift
Swift-style variadics
Nested types
Curried functions
https://developer.apple.com/library/ios/documentation/Swift/
Conceptual/BuildingCocoaApps/MixandMatch.html#//apple_ref/doc/
uid/TP40014216-CH10-ID122

21. Adding
New
Controller
Refactor
Existing
Controller1 2
Where to use Swift
in the beginning?
It`s ok to build a parallel universe

22. Find New Solutions™
and yeah, use guard…

23. Swift will make
your life easier
title = ~"Select Title"
Custom Operator for i18n

24. struct Storyboard {
struct Segues {
static let channelInfo = "channelInfo"
}
struct Cells {
static let channelCell = "channelCell"
}
struct ReuseView {
static let sectionHeader = "header"
}
}
Swift will make
your life easier
Define Segues, Identifier, and so forth

25. Swift will make
your life easier
@IBOutlet weak var myCellView: UIView! {
didSet {
myCellView.backgroundColor = .redColor()
myCellView.layer.masksToBounds = true
myCellView.layer.cornerRadius = 2
}
}
Configure Views after outlet binding

26. override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
switch (segue.identifier, segue.destinationViewController,
collectionView?.indexPathsForSelectedItems()?.first) {
case let(Storyboard.Segues.info?, controller as InfoController, index?):
controller.channel = channels?.get(index.row)
default:
break
}
}
Swift will make
your life easier
Pattern Match Your Life

27. Swift will make
your life easier
for (a, b) in (0...2).zipWithFollower() {
print(a, b) // 0,1 1,2 2,nil
}
public struct ZipWithFollower<T: SequenceType>: SequenceType {
public typealias Generator = AnyGenerator<(T.Generator.Element, T.Generator.Element?)>
let sequence: T
public init(_ sequence: T) {
self.sequence = sequence
}
public func generate() -> Generator {
var generator1 = sequence.generate()
var generator2 = sequence.generate()
_ = generator2.next()
return anyGenerator {
guard let element1 = generator1.next() else {
return nil
}
return (element1, generator2.next())
}
}
}
Clean up your control flow

28. struct StateFlow<S,T> {
let at: S
let to: T -> S
}
let wizardFlow: [StateFlow<WizardState, WizardConfig>] = [
from(.Init).to { config in
if config.useCustomSeletion {
return .ComponentWizard
}
return .ComponentSelection
}
]
Swift will make
your life easier
Double Down on Types

29. @elmkretzer
Go Swift!
www.symentis.com