Kotlin in production for 2 years, my learnings

Transcript

1. Welcome to GDG DUS July
2. Kotlin in production One year later Pascal Welsch, grandcentrix GmbH
3. Our existing JVM languages are great, but none of them have demonstrated the potential to become the de facto language of choice for a large percentage of JVM developers. - Joe Kutner - Heroku
5. How I started with Kotlin • Read the documentation • Did the Kotlin Kohans • Solved a few coding challenges with kotlin ◦ Google Code Jam ◦ Advent of Code • Kotlin Slack community is very helpful • Convert Java code to learn how to write it in Kotlin
7. How I started with Kotlin • Started writing new features in Kotlin • Migrated code (mostly manually)
8. • Wohin Du Willst - Android App - live ◦ Existing project written in java • Nearby Debugger - Android App - live ◦ Small app entirely in kotlin • Internal Technical Prototype - Android App - not released ◦ 98% in kotlin • GitVersioner Plugin - Gradle Plugin - live ◦ Written in kotlin • Current Client Project - Android App - not released ◦ Pure kotlin Last years projects
9. Gradle Plugin • Fast releases when Android Studio upgrades ◦ Will get better with the official support • Better use
10. Kotlin major releases • No pain! • Works 99% on day 1 • Long EAP and beta program • Tip: Don’t upgrade on day 1, wait for patch 1 or 2
11. Method count • org.jetbrains.kotlin:kotlin-stdlib-jre7:1.1.3-2 ◦ 6317 • io.reactivex.rxjava2:rxjava:2.1.1 ◦ 10204 • Io.reactivex:rxjava:1.3.0 ◦ 5751
12. RxJava is harder to learn than Kotlin
13. Mixing Kotlin and Java • Calling back and forth works! • NullPointerException still possible when using Java libs • Don’t use retrolambda for Interfaces in Kotlin
14. Lambdas <3 • So much better than Java lambdas
15. Multi dimensional arrays • Manual initialization required was required • Kind of a bummer when starting • New initializer function added in Kotlin 1.1
16. Data classes
17. Keep Multithreading in mind
18. Keep Multithreading in mind
19. Keep Multithreading in mind
20. Keep Multithreading in mind
21. Keep Multithreading in mind
22. No static • Global variable definitions • Global function definitions • Global objects • Companion objects • Except for Java, most languages have a way to declare constants without wrapping them in a class
23. No static
24. No SAM conversion for Kotlin interfaces • Solutions: ◦ write two methods, one for kotlin, one for Java ◦ Return Unit in Java code ◦ Write Interfaces in Java • Most requested feature in recent developer survey
25. No SAM conversion for Kotlin interfaces
26. Properties • No getters, setters required (optional) • Properties can by dynamic
27. Properties
28. Optional and named Parameters
29. Annotations processors • Completely unstable. Kapt barely works, only works every 5. Release • I stopped using Dagger2 -> Migrated to KoDeIn
30. KoDeIn
31. Reified Generics • Makes injection easy
32. Protobuf code generation • compile task order of protobuf plugin for doesn’t work with kotlin plugin • Can’t reference Protobuf classes from Kotlin code • Solution: Separate module for Protobuf code required
33. Bit shifting • Handling low level bits and bytes in Java was annoying • It got worse in Kotlin • Extension functions help a lot • Jetbrains is working on better bit shifting syntax and unsigned data types
34. Extension functions • Use a ActivityExt.kt file for Activity extension function • Use private where possible
35. Public by default • I would prefer internal by default • I always forget private for properties
36. Testing library • I’m still using AssertJ ◦ >5 assertion libs out there, non dominates, not really better • Mockito-kotlin helps with generics
37. Use IntelliJ for non Android projects • AS 2.3 has problems running tests for pure kotlin projects
38. Adoption of Kotlin at grandcentrix • We had a GO from management to use Kotlin in all projects one week before it was officially adopted by Google • Now we roll it out in all active projects over the next months • Starting with Unit Tests and new features
39. Coroutines • Beta in Kotlin 1.1 • Cool idea for async/await implementations • Useful for server side code to replace Promises • On Android RxJava is a better fit than coroutines
40. DSL feature • Gradle scripts can be written with kotlin (.kts)
41. Kotlin libraries • Write Android libraries in Java • Maybe release a separate kt artifact
42. JVM is stable • I tried Swift with generics and got a segmentation fault • I started to love the JVM
43. Pascal Welsch @passsy grandcentrix.net @grandcentrix