Discover what's new in Kotlin 1.2: syntax, standard library, performance and , of course, "Multiplatform project". Take closer look at how Kotlin authors see way of reusing code between platforms.

1. Kotlin 1.2
Sharing Code Between Platforms
Kirill Rozov
Android Developer

2. Kotlin Achievements
* Based on information from Stackoverflow
** In development

3. Kotlin Achievements
• Official language on Android
* Based on information from Stackoverflow
** In development

4. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
* Based on information from Stackoverflow
** In development

5. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
• Support in Spring 5.0
* Based on information from Stackoverflow
** In development

6. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
• Support in Spring 5.0
• Gradle Kotlin DSL
* Based on information from Stackoverflow
** In development

7. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
• Support in Spring 5.0
• Gradle Kotlin DSL
• Fastest-growing and one of the least-disliked languages*
* Based on information from Stackoverflow
** In development

8. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
• Support in Spring 5.0
• Gradle Kotlin DSL
• Fastest-growing and one of the least-disliked languages*
• Support of JVM, JS, Native**
* Based on information from Stackoverflow
** In development

9. Kotlin Achievements
• Official language on Android
• More than 17% projects in Android Studio 3.0
• Support in Spring 5.0
• Gradle Kotlin DSL
• Fastest-growing and one of the least-disliked languages*
• Support of JVM, JS, Native**
• Kotlin Conf
* Based on information from Stackoverflow
** In development

10. Kotlin Popularity
1.11.0

11. Language
syntax

12. Array literals
// Kotlin 1.1
@CacheConfig(cacheNames = arrayOf("books", "default"))
class BookRepository

13. Array literals
// Kotlin 1.1
@CacheConfig(cacheNames = arrayOf("books", "default"))
class BookRepository
The array literal syntax is constrained to annotation arguments
// Kotlin 1.2
@CacheConfig(cacheNames = ["books", “default"])
class BookRepository

14. lateinit
lateinit var lateinitVar: String
// ‘false’
println("isInitialized: " + this::lateinitVar.isInitialized)
lateinitVar = "value"
// ‘true’
println("isInitialized: " + this::lateinitVar.isInitialized)

15. lateinit
• Possibility to check whether lateinit variable is initialized
• Support on top-level properties
• Support for local variables

16. Inline functions
// Kotlin 1.1
fun <E> Iterable<E>.strings() = strings { it.toString() }
inline fun <E> Iterable<E>.strings(transform: (E) -> String) =
map { transform(it) }

17. Inline functions
// Kotlin 1.1
fun <E> Iterable<E>.strings() = strings { it.toString() }
inline fun <E> Iterable<E>.strings(transform: (E) -> String) =
map { transform(it) }
// Kotlin 1.2
inline fun <E> Iterable<E>.strings(
transform: (E) -> String = { it.toString() }) =
map { transform(it) }

18. Casts improvements
// Kotlin 1.1
val button = findViewById<View>(R.id.button) as Button

19. Casts improvements
// Kotlin 1.1
val button = findViewById<View>(R.id.button) as Button
// Kotlin 1.2
val button = findViewById(R.id.button) as Button

20. Casts improvements
// Kotlin 1.1
val s : Any = …
val firstChar = (s as? CharSequence)?.firstOrNull()
if (firstChar != null) {
s as CharSequence
return s.count { it == firstChar }
}

21. Casts improvements
// Kotlin 1.2
if (firstChar != null) {
// s: Any is smart cast to CharSequence
return s.count { it == firstChar }
}
// Kotlin 1.1
val s : Any = …
val firstChar = (s as? CharSequence)?.firstOrNull()
if (firstChar != null) {
s as CharSequence
return s.count { it == firstChar }
}

22. Standard
library

23. Standard library

24. Standard library
• Compatibility with Java 9 module system

25. Java 9 Support
• Compatible with the Java 9 module system (Project Jigsaw)
New artifacts kotlin-stdlib-jdkN
• Deprecated declaration in kotlin.reflect package were
removed
Use declarations in kotlin.reflect.full package instead

26. Standard library
• Compatibility with Java 9 module system

27. Standard library
• Compatibility with Java 9 module system
• New extensions for collections

28. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
Only for Iterable<T>, Sequence<T>, CharSequence

29. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
items.chunked(3) // [[1, 1, 2], [3]]
Only for Iterable<T>, Sequence<T>, CharSequence

30. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
items.chunked(3) // [[1, 1, 2], [3]]
items.chunked(2) { (x, y) -> Pair(x, y) } // [(1, 1), (2, 3)]
Only for Iterable<T>, Sequence<T>, CharSequence

31. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
items.chunked(3) // [[1, 1, 2], [3]]
items.chunked(2) { (x, y) -> Pair(x, y) } // [(1, 1), (2, 3)]
items.windowed(2) // [[1, 1], [1, 2], [2, 3]]
Only for Iterable<T>, Sequence<T>, CharSequence

32. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
items.chunked(3) // [[1, 1, 2], [3]]
items.chunked(2) { (x, y) -> Pair(x, y) } // [(1, 1), (2, 3)]
items.windowed(2) // [[1, 1], [1, 2], [2, 3]]
items.windowed(2) { it.average() } // [1, 1.5, 2.5]
Only for Iterable<T>, Sequence<T>, CharSequence

33. chuncked, windowed, zipWithNext
val items = listOf(1, 1, 2, 3)
items.chunked(3) // [[1, 1, 2], [3]]
items.chunked(2) { (x, y) -> Pair(x, y) } // [(1, 1), (2, 3)]
items.windowed(2) // [[1, 1], [1, 2], [2, 3]]
items.windowed(2) { it.average() } // [1, 1.5, 2.5]
items.zipWithNext { a, b -> b - a } // [0, 1, 1]
Only for Iterable<T>, Sequence<T>, CharSequence

34. fill, replaceAll, shuffle
val items = mutableListOf(0, 1, 2, 3, 5, 8)
Only for MutableList<T>

35. fill, replaceAll, shuffle
val items = mutableListOf(0, 1, 2, 3, 5, 8)
items.shuffle() // [3, 8, 5, 0, 2, 1]. Output can be different
Only for MutableList<T>

36. fill, replaceAll, shuffle
val items = mutableListOf(0, 1, 2, 3, 5, 8)
items.shuffle() // [3, 8, 5, 0, 2, 1]. Output can be different
items.replaceAll { it * 2 } // [0, 2, 4, 6, 10, 16]
Only for MutableList<T>

37. fill, replaceAll, shuffle
val items = mutableListOf(0, 1, 2, 3, 5, 8)
items.shuffle() // [3, 8, 5, 0, 2, 1]. Output can be different
items.replaceAll { it * 2 } // [0, 2, 4, 6, 10, 16]
items.fill(5) // [5, 5, 5, 5, 5, 5]
Only for MutableList<T>

38. Standard library
• Fully compatibility with Java 9 module system
• New extensions for collections

39. Standard library
• Fully compatibility with Java 9 module system
• New extensions for collections
• Math operations

40. Standard library
• Fully compatibility with Java 9 module system
• New extensions for collections
• Math operations
• Operators and conversions for BigInteger and BigDecimal
• Floating point to bits conversions
• Regex is now Serializable
• Closeable.use() calls Throwable.addSuppressed() (JDK 7+)

41. Java
• Constructor calls normalization
• Java-default methods calls
• Breaking changes:
• Consistent behaviour of x.equals(null) for platform types
• Added check of receiver in inline extension functions that
were called on a null value of a platform type
• Smart cast inside try block after the block made more strict

42. Deprecation
• Mutating backing field of read-only property
• Override copy() in data classes
• Not inner classes in enum entries
• Passing a single item for a vararg parameter in the named
form
• Inner classes of generic classes extending Throwable

43. Other
• Support for ::foo as a shorthand for this::foo
• JS TypedArrays support for Kotlin primitive array (IntArray,
FloatArray, etc) enabled by default
• The Kotlin compiler now provides an option to treat all
warnings as errors
• Support in Kotlin Native 0.4

44. Compilation Performance
Approximately 25% improvement over Kotlin 1.1

45. Multiplatform
projects

46. Multiplatform Projects

47. expect & actual
// expected platform-specific API
expect fun hello(world: String) Common
// actual JVM implementation
actual fun hello(world: String) =
println(“Hello, $world, on the JVM!") JVM
// actual JS implementation
actual fun hello(world: String) =
console.log("Hello, $world, on the JS!") JS

48. expect class Date() {
fun getDate(): Int
fun getMonth(): Int
} Common
actual class Date {
private val calendar: Calendar
actual constructor() {
calendar = Calendar.getInstance()
}
actual fun getDate() = calendar[DAY_OF_MONTH]
actual fun getMonth() = calendar[MONTH]
} JVM
actual external class Date {
actual fun getDate(): Int
actual fun getMonth(): Int
} JS

49. Common
module
Platform
module
Regular
module

50. Common
module
JVM
JS

51. //common-jvm/build.gradle
apply plugin:'kotlin-platform-jvm'
dependencies {
compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
expectedBy project(":common")
} JVM
//android/build.gradle
apply plugin: 'kotlin-android'
dependencies {
implementation project(":common-jvm")
} Android
//common/build.gradle
apply plugin: 'kotlin-platform-common'
dependencies {
compile "org.jetbrains.kotlin:kotlin-stdlib-common:$kotlin_version"
}
Common

52. Common modules
• Test
Run test both on Java & JS platforms
• Serialization
Marshal Kotlin objects between different tiers of your application, based on JSON or ProtoBuf as
serialization format
• HTML
The same code to render HTML in the backend and in the frontend

53. Future commons
• IO
• Networking (HTTP, TCP, etc.)
• Dates

54. Summary

55. Summary
• Allow to write parts of app in same language

56. Summary
• Allow to write parts of app in same language
• Interoperability on supported platforms

57. Summary
• Allow to write parts of app in same language
• Interoperability on supported platforms
• Shared business logic

58. Summary
• Allow to write parts of app in same language
• Interoperability on supported platforms
• Shared business logic
• UI is platform-specific

59. Summary
• Allow to write parts of app in same language
• Interoperability on supported platforms
• Shared business logic
• UI is platform-specific
• JVM/JS code reuse already worked, Native coming soon

60. Summary
• Allow to write parts of app in same language
• Interoperability on supported platforms
• Shared business logic
• UI is platform-specific
• JVM/JS code reuse already worked, Native coming soon
• Support of Multiplatform projects in IDEA 2017.3

61. Thanks
krl.rozov@gmail.com