JavaOne2012: Kotlin: Practical Aspects of JVM Language Implementation

Kotlin: How Things Work Practical Aspects of JVM Language Implementation Andrey BreslavTuesday, October 2, 12

Why you should care • Language is an abstraction ➡ thus it leaks abstraction • When something weird happens ➡ you may need to "see through the Matrix" 2Tuesday, October 2, 12

tetris is way too easy when played this way 3Tuesday, October 2, 12

JVM & Its Languages Whats i n... otl e , K possible? sur Clo vy, G roo , Sc ala Java t 1995 2012 4Tuesday, October 2, 12

About Me • Project lead of Kotlin ➡ at JetBrains since 2010 (not (RICH HICKEY)) • EG member of JSR-335 ➡ Project Lambda 5Tuesday, October 2, 12

Kotlin Modern Language for Industry • Smart compiler • Static typing ➡ Less boilerplate • Readability • Flexible abstractions • Tool support ➡ Powerful libraries • Interoperability 6Tuesday, October 2, 12

Outline • Extensions • Bridges of All Sorts • Types: Collections and Nulls • Dreams... (maybe) 7Tuesday, October 2, 12

Extensions • Live Demo ➡ Extension syntax ➡ How it is compiled ➡ Multiple files in a package 8Tuesday, October 2, 12

Bridges 9Tuesday, October 2, 12

Bridges for Generics (Lj/l/Object;)Lj/l/Object; overrides (I)I (Lj/l/Object;)Lj/l/Object; "synthetic bridge method" (JLS) 10Tuesday, October 2, 12

Kotlin Brides & Primitives Java 1 1 & Kotlin Kotlin foo(t: T) = t foo(t: Int) = t 1 1 11Tuesday, October 2, 12

Default Arguments 12Tuesday, October 2, 12

Masks for Defaults foo(a, b) foo(a, b, mask: Int) if (mask & 1) a = 0 if (mask & 2) b = 0 foo(a, b) 13Tuesday, October 2, 12

Traits: Code in Interfaces class Trait$Impl { static foo()V { println("Hi") } } 14Tuesday, October 2, 12

Trait Hierarchy T1 foo() { println() } T2 foo() { T1$Impl.foo() } C foo() { T2$Impl.foo() } 15Tuesday, October 2, 12

Summary • Sometimes you need just one more method... 16Tuesday, October 2, 12

Collections How Data-Compatible is Your Language?Tuesday, October 2, 12

Collections & Variance Java: Kotlin: 18Tuesday, October 2, 12

Kotlins Collections 19Tuesday, October 2, 12

Declaration-Site Variance 20Tuesday, October 2, 12

Translation Ø java.util.List 21Tuesday, October 2, 12

Translation: Inheritance 22Tuesday, October 2, 12

Translation: Variance 23Tuesday, October 2, 12

Calling Java From Kotlin 24Tuesday, October 2, 12

Summary • Kotlins collections ➡ Better than Javas ➡ Still Compatible 25Tuesday, October 2, 12

Nullable TypesTuesday, October 2, 12

Demo • Kotlin is null-safe • Java code can be annotated for safe access 27Tuesday, October 2, 12

Talk Summary • Languages are about tradeoffs • Kotlin is cool :) 28Tuesday, October 2, 12

Kotlin Resources • Docs: http://kotlin.jetbrains.org • Demo: http://kotlin-demo.jetbrains.com • Code: http://github.com/jetbrains/kotlin • Twitter: ➡ @project_kotlin ➡ @abreslav 29Tuesday, October 2, 12

JavaOne2012: Kotlin: Practical Aspects of JVM Language Implementation

by Andrey Breslav on Oct 05, 2012

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