KMP with non-Kotlin languages (Droidcon NYC 2025)

Kotlin multiplatform is a great way to share new and existing Kotlin code with other platforms. But what about non-Kotlin code? Turns out Kotlin multiplatform can also be a great way to share code from other languages such as Swift, Rust, Zig, C, and more. This talk will show how to adapt code from these other languages into KMP, the restrictions and considerations when doing so, and look at some existing libraries which are doing this today.

Video: coming soon

Transcript

1. Jake Wharton Jake Wharton Jake Wharton Jake Wharton KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages New Yorker / Bettmann / Getty
2. Not all libraries are written in Kotlin
3. Not all libraries should be written in Kotlin
4. The best libraries are not written in Kotlin
5. The best libraries can still be used in Kotlin
6. platfo rmL og("Hey")
7. platfo rmL og("Hey")
8. platfo rmL og("Hey") expect fun platfo rmL og( message: String, )
9. platfo rmL og("Hey") expect fun platfo rmL og( message: String, ) actual fun platfo rmL og( message: String, ) { Log.d(TAG, message) }
10. platfo rmL og("Hey") expect fun platfo rmL og( message: String, ) actual fun platfo rmL og( message: String, ) { NSLog(message) }
11. platfo rmL og("Hey") expect fun platfo rmL og( message: String, ) actual fun platfo rmL og( message: String, ) { console.log(message) }
12. platfo rmL og("Hey") expect fun platfo rmL og( message: String, ) actual fun platfo rmL og( message: String, ) { LOGGER.log(message) }
13. platfo rmL og("Hey") expect fun platfo rmL og( message: String, ) actual fun platfo rmL og(…) {…} actual fun platfo rmL og(…) {…} actual fun platfo rmL og(…) {…} actual fun platfo rmL og(…) {…}
14. platfo rmL og("Hey")
15. Row { Button( text = "Hey", onClick = { println("Sup") }, ) }
16. Row { Button( text = "Hey", onClick = { println("Sup") }, ) }
17. Row { Button( text = "Hey", onClick = { println("Sup") }, ) }
19. Skiko Walkthrough
20. skia .so
21. .cpp skia .so skiko .so
22. kotlinc .kt .cpp skia .so skiko .so
23. kotlinc linking .klib .kt .cpp skia .so skiko .so .jar
25. 2016 2019 2022 2023
26. interface NaturalLanguageDateParser { fun parse(input: String): LocalDate }
27. class DateParser Im pl : NaturalLanguageDateParser { fun parse(input: String): LocalDate { return // … } } interface NaturalLanguageDateParser { fun parse(input: String): LocalDate }
28. class DateParser Im pl : NaturalLanguageDateParser { fun parse(input: String): LocalDate { return // … } } zipline.bind( name = "nlDateParser", instance = NaturalLanguageDateParser Im pl(), ) interface NaturalLanguageDateParser { fun parse(input: String): LocalDate }
29. class DateParser Im pl : NaturalLanguageDateParser { fun parse(input: String): LocalDate { return // … } } zipline.bind( name = "nlDateParser", instance = NaturalLanguageDateParser Im pl(), ) interface NaturalLanguageDateParser { fun parse(input: String): LocalDate }
30. class DateParser Im pl : NaturalLanguageDateParser { fun parse(input: String): LocalDate { return // … } } zipline.bind( name = "nlDateParser", instance = NaturalLanguageDateParser Im pl(), ) interface NaturalLanguageDateParser { fun parse(input: String): LocalDate } val parser = zipline.take( name = "nlDateParser", )
31. class DateParser Im pl : NaturalLanguageDateParser { fun parse(input: String): LocalDate { return // … } } zipline.bind( name = "nlDateParser", instance = NaturalLanguageDateParser Im pl(), ) interface NaturalLanguageDateParser { fun parse(input: String): LocalDate } val parser = zipline.take( name = "nlDateParser", ) println( parser.parse( "Next Tuesday", ), )
32. Zipline Walkthrough
33. cinterop cklib zipline .h .c Android cmake zig cc
34. cinterop linking .klib cklib zipline .h .c .kt Android cmake zig cc kotlinc
35. cinterop linking .klib JNI .cpp cklib zipline .h .c .kt Android cmake zig cc kotlinc
36. cinterop linking .klib JNI .cpp cklib zipline .h .c .kt Android cmake zig cc kotlinc
37. cinterop linking .klib JNI .cpp .so .jar cklib zipline .h .c .kt Android cmake zig cc .so .aar kotlinc
38. Mosaic Walkthrough
39. mosaic .c .h cklib cinterop
40. mosaic .c .h cklib cinterop linking .klib .kt kotlinc
41. JNI .h javac JNI .java
42. kotlinc .kt JNI .h javac JNI .java .jar
43. kotlinc .kt .c .h .so JNI .h zig cc javac JNI .java JNI .c .jar
44. kotlinc .kt .c .h .so JNI .h jextract zig cc javac JNI .java JNI .c .jar
45. kotlinc .kt .c .h .so JNI .h jextract zig cc javac JNI .java JNI .c .jar kotlinc JDK22 .kt
46. JNI .h javac JNI .java JNI .c kotlinc JDK22 .kt jextract .c .h zig cc .so .jar kotlinc .kt
47. Sample Walkthrough
48. The best libraries can still be used in Kotlin
49. Designed by Freepik Jake Wharton Jake Wharton Jake Wharton Jake Wharton KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages KMP wi th non-Kotlin languages New Yorker / Bettmann / Getty 100% NATURAL F R E S H I N G R E D I E N T S T H I S P R O D U C T I S 100% N A T U R A L F R E S H I N G R E D I E N T S N O A I B U L L S H I T