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

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Lessons learned from porting to Swift and Kotlin by Ellen Shapiro Mobile Era | Oslo, Norway | October 2017 @designatednerd | justhum.com | designatednerd.com

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(this is awkward)

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!""

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!"#

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!"#

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ANYWAY

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Android

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iOS

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iOS (excluding dependencies)

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Step 1 Selling it to The Bosses

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Identify speciﬁc problems addressed by the new language

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Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; }

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Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; } iOS 9 = !

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Objective-C if (![paymentNetworks containsObject:PKPaymentNetworkDiscover]) { [paymentNetworks addObject:PKPaymentNetworkDiscover]; } iOS 8 = !

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Swift if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) }

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Swift if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } !" Does Not Compile

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Swift if @available(iOS 9.0, *) { if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } }

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Swift if @available(iOS 9.0, *) { if !paymentNetworks.contains(.discover) { paymentNetworks.append(.discover) } } Safe at compile time and run time

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Be honest about potential drawbacks

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Be honest (with yourself) about potential drawbacks

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Step 2 Start small

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Step 2 Start small

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Learn the new language

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Fight New System APIs or A New Language not both at once

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Stop writing old language patterns in a new language

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Objective-C NSMutableArray *capitalizedStrings = [NSMutableArray array]; for (NSString *string in arrayOfStrings) { NSString *thing = [string capitalized]; [capitalizedStrings addObject: thing]; }

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Objective-C, but written in Swift var capitalizedStrings = [String]() for string in arrayOfStrings { let thing = string.capitalized capitalizedStrings.append(thing) }

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Swiftier let capitalizedStrings = arrayOfStrings.map { string in let thing = string.capitalized return thing }

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Swiftier let capitalizedStrings = arrayOfStrings.map { string in let thing = string.capitalized return thing } Swiftiest let capitalizedStrings = arrayOfStrings.map { $0.capitalized }

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Limit your risk

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A parable of going too far, too fast

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Be willing to pause and re-evaluate (before everything goes wrong)

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Be willing to pause and re-evaluate (before everything goes wrong)

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Step 3 Biggest ! For Your "

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Step 3 Biggest ! For Your "

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Look at your bugs and crashes

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NPE

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NPE + GoogleMaps

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Look at your most error-prone code

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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; }

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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; }

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Swift 4 JSON Parsing static func from(jsonData: Data) -> User? { let decoder = JSONDecoder() return try? decoder.decode(User.self, for: jsonData) }

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(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 } }

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Step 4 Advanced Features for Fun and Proﬁt

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Step 4 Advanced Features for Fun, Maintainability, and Proﬁt

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Make your code more reusable

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Swift: Protocols!

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Kotlin: Extensions!

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Make your code safer

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Swift: Version handling!

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Kotlin: XML ids Become automatic variables

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activity_profile.xml 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"); }

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activity_profile.xml 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"); }

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activity_profile.xml 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" }

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Things You Should Do at Every Step

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Test

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Seriously though, Test

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What was I even trying to do here?

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Share strategies

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Share beneﬁts

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Share problems

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Review

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Learn by reading

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Keep code clear

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Swiftiest let capitalizedStrings = arrayOfStrings.map { $0.capitalized }

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Unnecessarily One-Liniest let studentNames = students.reduce("") { $0 + "\n" + ($1.firstName ?? "") + " " + ($1.lastName ?? "") }

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! Borderline Incomprehensible ! array.flatMap { $0 } .map { $0.doSomething() } .flatMap { $0 } .filter { $0.isSomething || $0.isSomethingElse } .reduce("") { $0 + $1.description }

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"I don't understand this code" != "I don't understand this language"

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Reducing confusion

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Listen to the creators

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Listen skeptically to the creators

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Watch out for Yaks

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Never let the perfect be the enemy of the shipping

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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!

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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/

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Links → Kotlin Android Extensions https://kotlinlang.org/docs/tutorials/android- plugin.html

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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

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Photo Credits → Paperwork, by Keith Williamson https://www.ﬂickr.com/photos/elwillo/4729801304 → Simpsons screenshots + memes, Frinkiac https://frinkiac.com/