Seattle Kotlin: Adopting Kotlin

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Adopting Kotlin A case study in team buy-in and adoption © @n8ebel, Udacity Engineering 2018 1

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What Is Kotlin? » a programming language developed by JetBrains » targets the JVM » is 100% compatible with Java for Android development © @n8ebel, Udacity Engineering 2018 2

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Where Is It Used? » Android » JVM » Browser » Backend » iOS © @n8ebel, Udacity Engineering 2018 3

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Adoption at Udacity © @n8ebel, Udacity Engineering 2018 4

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Production Today Have been using in production for over a year Today, Kotlin is our primary development language for Android © @n8ebel, Udacity Engineering 2018 5

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Why Invest In Kotlin? » Our adoption process » How are we using Kotlin today » Tips for incorporating Kotlin into your project © @n8ebel, Udacity Engineering 2018 6

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Why Kotlin? © @n8ebel, Udacity Engineering 2018 7

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“Kotlin provides a more enjoyable developer experience by allowing us to express our features & ideas using safer, more concise code. This, in turn, enables us to build a better product for our users” © @n8ebel, Udacity Engineering 2018 8

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Key Beneﬁts » Improved crash rate » Reduction in lines of code written » Decreased time spent in code review » Renewed excitement around experimentation and innovation © @n8ebel, Udacity Engineering 2018 9

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Ultimately, our goal is to provide our users with the best learning experience possible. © @n8ebel, Udacity Engineering 2018 10

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We believe Kotlin helps us do that. © @n8ebel, Udacity Engineering 2018 11

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How Did We Start? © @n8ebel, Udacity Engineering 2018 12

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Recognition of Pain Points We started to notice patterns in our code reviews » “we need to be consistent in our handling of null” » “this code could be shortened using a more functional approach” © @n8ebel, Udacity Engineering 2018 13

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Recognition of Pain Points Having experimented with Kotlin outside Udacity, we knew the language could help with some of these issues © @n8ebel, Udacity Engineering 2018 14

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Kotlin, Meet the Team » built a small new feature » create both a Java & Kotlin PR » demonstrated that Kotlin could be easily integrated © @n8ebel, Udacity Engineering 2018 15

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Jumping Off Point » Set out to migrate our Settings screen » During testing, we looked closely for 2 things © @n8ebel, Udacity Engineering 2018 16

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Jumping Off Point 1.Usability issues: what impact did Kotlin have on crashes/bugs? 2.Development process: did Kotlin cause CI issues, slow down our build, or slow down feature development? © @n8ebel, Udacity Engineering 2018 17

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Ship It As expected, no signiﬁcant issues found Released to production © @n8ebel, Udacity Engineering 2018 18

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Slow Down At this point, we slowed down a bit. We loved using Kotlin, but recognized the potential risks of going all-in on an unofﬁcially supported language. We continued to add/convert some tests to Kotlin, but no new feature code was using it © @n8ebel, Udacity Engineering 2018 19

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Game Changer © @n8ebel, Udacity Engineering 2018 20

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Google I/O The Google I/O announcement of ofﬁcial support for Kotlin was the push we needed We decided immediately that we wanted to go all-in on Kotlin © @n8ebel, Udacity Engineering 2018 21

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Team Buy In Met with our PM and expressed our desire/plan to adopt Kotlin. We were met with a healthy dose of pragmatism. © @n8ebel, Udacity Engineering 2018 22

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“What’s the value prop?” » Is the language stable/safe to be using now? » Will it slow down development? » Are there tangible beneﬁts? © @n8ebel, Udacity Engineering 2018 23

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Migration Plan © @n8ebel, Udacity Engineering 2018 24

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Migration Plan 1.All new dev work in Kotlin 2.If anything larger than a small bug ﬁx must be done to a class, consider migrating the class to Kotlin 3.Start migrating existing code © @n8ebel, Udacity Engineering 2018 25

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Migration Plan Planned to tackle the low hanging fruit ﬁrst (utilities, helpers, isolated classes) Work towards migrating enough code that the majority of our daily development would be in Kotlin © @n8ebel, Udacity Engineering 2018 26

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Migration Process » Started by using the Java to Kotlin conversion tool within Android Studio » Then made manual adjustments to the converted code © @n8ebel, Udacity Engineering 2018 27

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Migration Process Some of the adjustments we made to converted code: » Avoiding the use of !! operator » When possible, convert helper methods to top-level functions » Avoid companion object where possible » Reorganize the generated code » Expressing code in a more Kotlin idiomatic way © @n8ebel, Udacity Engineering 2018 28

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Handling null In many places we focused on leveraging statements such as object?.let {...} instead of if(object != null) { ... } © @n8ebel, Udacity Engineering 2018 29

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stdlib Tried to leverage the great collections stdlib that Kotlin provides. Allowed us to replace large blocks of code with a few lines of concise functional code © @n8ebel, Udacity Engineering 2018 30

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Shorter, safer code val recentQueries:List? = listOf() val recentsToDisplay = recentQueries ?.ﬁlterNotNull() ?.ﬁlter{ it.isNotBlank() } ?.take(5) ?: listOf() © @n8ebel, Udacity Engineering 2018 31

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Where Are We Today? © @n8ebel, Udacity Engineering 2018 32

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Flagship App Our ﬂagship codebase continues to be migrated to Kotlin » ~40% Kotlin today » All new dev work is done in Kotlin © @n8ebel, Udacity Engineering 2018 33

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New Codebase Additional code base that is 100% Kotlin » Allowed us to fully explore the language » Have began using several language features extensively © @n8ebel, Udacity Engineering 2018 34

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New Codebase Began leveraging more interesting aspects of the language » data classes » sealed classes » named arguments & default parameter values » higher order functions © @n8ebel, Udacity Engineering 2018 35

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Tips for Incorporating Kotlin » If new to the language, start with the conversion tool » Don’t be afraid to further modify the converted code © @n8ebel, Udacity Engineering 2018 37

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Tips for Incorporating Kotlin Start with tests - can help work out build issues - explore basic syntax - great for understanding interop story Features - writing feature code will give a more comprehensive picture of how it can affect your code © @n8ebel, Udacity Engineering 2018 38

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Tips for Incorporating Kotlin Don’t go wild trying to write “idiomatic” Kotlin. - As you progress with the language, it’s likely your opinion of whats readable vs what’s possible will evolve © @n8ebel, Udacity Engineering 2018 39

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Tips for Incorporating Kotlin » As you migrate existing code, re-visit previously converted code from time to time. You may ﬁnd that newly discovered conventions/patterns could be applied. » Don’t forget to thoroughly test any interop layers between Java and Kotlin. Nullability issues can crop up during runtime when dealing with nullable platform types. © @n8ebel, Udacity Engineering 2018 41

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How Can Kotlin Improve Your Product? take advantage of this period of exploration while learning the language © @n8ebel, Udacity Engineering 2018 43

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How Can Kotlin Improve Your Product? Question existing patterns/conventions for writing Android apps and ask yourself if/how Kotlin might enable you to write alternative solutions © @n8ebel, Udacity Engineering 2018 44

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How Can Kotlin Improve Your Product? » can your code be refactored to avoid null properties? » can you replace helper classes/methods with top- level functions? » can you avoid handling null properties by using a delegate? » could a logical path be expressed using functional concepts to reduce a class’s state? © @n8ebel, Udacity Engineering 2018 45

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Conﬁdent Moving Forward We feel great about our investment into Kotlin » Google continues to poor resources into Kotlin » Samples now defaulting to Kotlin » New ktx library for Android » Increased interest from users will accelerate improvements © @n8ebel, Udacity Engineering 2018 47

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More From Udacity Free Course - Kotlin for Android Developers Engineering Blog Posts* - Adopting Kotlin - Learning Kotlin by Mistake - Modeling ViewModel States Using Kotlin’s Sealed Classes © @n8ebel, Udacity Engineering 2018 48