Lessons Learned From Porting To Swift And Kotlin - Mobile Era Oslo, October 2017

Video:
https://vimeo.com/237875498

Abstract:
SpotHero has been moving its entire iOS application to Swift and started moving its Android app to Kotlin. Here's some lessons learned in the process in terms of selling management on using a new languages, how to get started, and some tips on things you should do along the way.

(Big thanks to my old crew at SpotHero!)

Transcript

1. Lessons learned from porting to Swift and Kotlin by Ellen Shapiro Mobile Era | Oslo, Norway | October 2017 @designatednerd | justhum.com | designatednerd.com
3. (this is awkward)
4. !
5. !
6. !""
7. !"#
8. !"#
9. !
10. !
13. ANYWAY
21. Android
22. iOS
23. iOS (excluding dependencies)
25. Step 1 Selling it to The Bosses
26. Identify specific problems addressed by the new language
27. Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; }
29. Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; } iOS 9 = !
30. Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; } iOS 8 = !
31. Swift if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) }
32. Swift if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } !" Does Not Compile
33. Swift if @available(iOS 9.0, *) { if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } }
34. Swift if @available(iOS 9.0, *) { if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } } Safe at compile time and run time
35. Be honest about potential drawbacks
36. Be honest (with yourself) about potential drawbacks
41. Step 2 Start small
42. Step 2 Start small
43. Learn the new language
44. Fight New System APIs or A New Language not both at once
45. Stop writing old language patterns in a new language
46. Objective-C NSMutableArray *capitalizedStrings = [NSMutableArray array]; for (NSString *string in arrayOfStrings) { NSString *thing = [string capitalized]; [capitalizedStrings addObject: thing]; }
47. Objective-C, but written in Swift var capitalizedStrings = [String]() for string in arrayOfStrings { let thing = string.capitalized capitalizedStrings.append(thing) }
48. Swiftier let capitalizedStrings = arrayOfStrings.map { string in let thing = string.capitalized return thing }
49. Swiftier let capitalizedStrings = arrayOfStrings.map { string in let thing = string.capitalized return thing } Swiftiest let capitalizedStrings = arrayOfStrings.map { $0.capitalized }
50. Limit your risk
51. A parable of going too far, too fast
59. Be willing to pause and re-evaluate (before everything goes wrong)
60. Be willing to pause and re-evaluate (before everything goes wrong)
61. Step 3 Biggest ! For Your "
62. Step 3 Biggest ! For Your "
63. Look at your bugs and crashes
64. NPE
65. NPE + GoogleMaps
66. Look at your most error-prone code
67. Objective-C JSON Parsing - (instancetype)fromJSONData:(NSData *)data { NSDictionary* jsonObject = [NSJSONSerialization jsonObjectWithData:data error:nil]; if (jsonObject == nil]) { return nil; } user.firstName = dictionary[@"first_name"]; user.lastName = dictionary[@"last_name"]; user.age = [dictionary[@"age"] integerValue]; return user; }
68. Objective-C JSON Parsing - (instancetype)fromJSONData:(NSData *)data { NSDictionary* jsonObject = [NSJSONSerialization jsonObjectWithData:data error:nil]; if (jsonObject == nil || ![jsonObject isKindOfClass:[NSDictionary class]]) { return nil; } if ([dictionary[@"first_name"] isKindOfClass: [NSString class]]) { user.firstName = dictionary[@"first_name"]; } else { return nil; } if ([dictionary[@"last_name"] isKindOfClass: [NSString class]]) { user.lastName = dictionary[@"last_name"]; } else { return nil; } if ([dictionary[@"age"] isKindOfClass: [NSNumber class]]) { user.age = [dictionary[@"age"] integerValue]; } else { return nil; } return user; }
69. Swift 4 JSON Parsing static func from(jsonData: Data) -> User? { let decoder = JSONDecoder() return try? decoder.decode(User.self, for: jsonData) }
70. (This does require some setup) struct User: Codable { let firstName: String let lastName: String let age: Int enum CodingKeys: String, CodingKey { case firstName = "first_name", lastName = "last_name", age } }
71. Step 4 Advanced Features for Fun and Profit
72. Step 4 Advanced Features for Fun, Maintainability, and Profit
73. Make your code more reusable
74. Swift: Protocols!
75. Kotlin: Extensions!
76. Make your code safer
77. Swift: Version handling!
78. Kotlin: XML ids Become automatic variables
79. activity_profile.xml <TextView android:id="@+id/textview_username" android:layout_width="fill_parent" android:layout_height="wrap_content" /> ProfileActivity.java TextView mUsernameTextView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.profile_activity); mUsernameTextView = (TextView) findViewById(R.id.textview_username); mUsernameTextView.setText("Hello, User"); }
80. activity_profile.xml <TextView android:id="@+id/textview_username" android:layout_width="fill_parent" android:layout_height="wrap_content" /> ProfileActivity.java @BindView(R.id.textview_username) TextView mUsernameTextView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.profile_activity); mUsernameTextView.setText("Hello, User"); }
81. activity_profile.xml <TextView android:id="@+id/textview_username" android:layout_width="fill_parent" android:layout_height="wrap_content" /> ProfileActivity.kt import kotlinx.android.synthetic.main.activity_profile.* public override fun onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_profile) textview_username.text = "Hello, User" }
82. activity_profile.xml <TextView android:id="@+id/usernameTextView" android:layout_width="fill_parent" android:layout_height="wrap_content" /> ProfileActivity.kt import kotlinx.android.synthetic.main.activity_profile.* public override fun onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_profile) usernameTextView = "Hello, User" }
83. Things You Should Do at Every Step
84. Test
86. Seriously though, Test
87. What was I even trying to do here?
88. Share
89. Share strategies
90. Share benefits
91. Share problems
92. Review
93. Learn by reading
94. Keep code clear
95. Swiftiest let capitalizedStrings = arrayOfStrings.map { $0.capitalized }
96. Unnecessarily One-Liniest let studentNames = students.reduce("") { $0 + "\n" + ($1.firstName ?? "") + " " + ($1.lastName ?? "") }
97. ! Borderline Incomprehensible ! array.flatMap { $0 } .map { $0.doSomething() } .flatMap { $0 } .filter { $0.isSomething || $0.isSomethingElse } .reduce("") { $0 + $1.description }
98. "I don't understand this code" != "I don't understand this language"
99. Reducing confusion
100. Listen to the creators
108. Listen skeptically to the creators
113. Watch out for Yaks
115. Never let the perfect be the enemy of the shipping
116. Obligatory Summary Slide → Honestly assess the pros and cons → Start small, then go bonkers once it works → Test the crap out of stuff in the new language → Share your code, your joy, and your pain → Resist desire to rewrite your whole app at once → Ship it!
117. Links → Concurrency In Swift: One Approach https://gist.github.com/lattner/ 31ed37682ef1576b16bca1432ea9f782 → Apple's Swift Blog https://developer.apple.com/swift/blog/ → Jetbrains' Kotlin Blog https://blog.jetbrains.com/kotlin/
118. Links → Kotlin Android Extensions https://kotlinlang.org/docs/tutorials/android- plugin.html
119. Videos → Anything You Can Do, I Can Do Better (Kickstarter team on FP in Kotlin vs. Swift) https://www.youtube.com/watch? v=_DuGaAkQSnM → iOS & Android & Swift & Kotlin (Stuart Kent on Kotlin for iOS Devs) http://www.stkent.com/2017/07/27/ios-and- android-and-swift-and-kotlin.html
120. Photo Credits → Paperwork, by Keith Williamson https://www.flickr.com/photos/elwillo/4729801304 → Simpsons screenshots + memes, Frinkiac https://frinkiac.com/