What's new in Kotlin?

1 . Beijing What’s new in Kotlin? Svetlana Isakova @sveta_isakova 

2 . Kotlin developers 3000 2250 2.2M 1500 750 700K 156K 0 2016 2017 2018 

3 . Timeline 2010 Project started … … 2016 Kotlin 1.0 2017 Official on Android 2018 Kotlin 1.3 

4 . Kotlin evolution Kotlin 1.0 Kotlin gets stable! Kotlin 1.1 Coroutines (experimental) Kotlin 1.2 Multi-platform projects (experimental) Kotlin/Native (experimental) Kotlin 1.3 Coroutines get stable! Multi-platform projects can target Kotlin/Native (experimental) 

5 . Agenda • Kotlin evolution • “Experimental” features 

6 .Agenda: experimental features • Inline Classes • Contracts • Channels • Flows • Multiplatform Projects 

7 . Principles of Pragmatic Evolution Language design is cast in stone, but this stone is reasonably soft, and with some effort we can reshape it later. Kotlin Design Team * The real sculpture made by José Manuel Castro López 

8 .Principles of Pragmatic Evolution • keeping the language modern • comfortable updates • feedback loop 

9 .KEEPing the language modern https://github.com/Kotlin/KEEP KEEP = Kotlin Evolution and Enhancement Process contains language proposals and the corresponding discussions 

10 . Comfortable updates • Deprecation warnings in advance • Automatic migration 

11 .Feedback loop with the community • Kotlin the community • Kotlin team listens to the community • The community members influence the Kotlin evolution 

12 .Contributors from all over the world … 

13 .Experimental features 

14 . Experimental features The goal: to let new features be tried by early adopters as soon as possible 

15 .Experimental Language Features • can be changed in the future • you need to explicitly opt in at the call site to use experimental features compileTestKotlin { kotlinOptions { freeCompilerArgs += "-Xinline-classes" } } 

16 . Experimental API for Libraries • can be publicly released as a part of the library • may break at any moment 

17 . Experimental API You can mark your new class or function as experimental @Experimental annotation class ShinyNewAPI @ShinyNewAPI class Foo { ... } 

18 .Using experimental API @UseExperimental(ShinyNewAPI::class) fun doSomethingImportant() { val foo = Foo() ... } 

19 . Experimental: Summary • feedback loop for new features and API 

20 .Inline classes 

21 . Inline classes • can wrap values without additional overhead • currently an experimental feature 

22 . Duration API • KEEP: Duration and Time Measurement API • status: experimental in Kotlin 1.3.50 • uses inline classes 

23 . Refining API: trying primitive args fun greetAfterTimeout(millis: Long) greetAfterTimeout(2) // meaning 2 seconds? 

24 . Refining API: trying primitive args fun greetAfterTimeout(millis: Long) greetAfterTimeout(2) // meaning 2 seconds? Too easy to make a mistake 

25 . Refining API: trying overloads fun greetAfterTimeoutMillis(millis: Long) fun greetAfterTimeoutSeconds(seconds: Long) greetAfterTimeoutSeconds(2) 

26 . Refining API: trying overloads fun greetAfterTimeoutMillis(millis: Long) fun greetAfterTimeoutSeconds(seconds: Long) greetAfterTimeoutSeconds(2) Too verbose 

27 . Refining API: trying class class Duration(val millis: Long) fun greetAfterTimeout(duration: Duration) greetAfterTimeout(Duration(millis = 2000)) 

28 . Refining API: trying class class Duration(val millis: Long) fun greetAfterTimeout(duration: Duration) greetAfterTimeout(Duration(millis = 2000)) Extra object is allocated 

29 . Inline classes to the rescue inline class Duration(val value: Long) fun greetAfterTimeout(duration: Duration) Under the hood: fun greetAfterTimeout_(duration: Long)