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Practical Aspects of JVM Language Implementation
Andrey Breslav
Kotlin: How Things Work
Tuesday, October 2, 12
Why you should care• Language is an abstraction
➡ thus it leaks
• When something weird happens➡ you may need to "see through the Matrix"
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abstraction
Tuesday, October 2, 12
3
tetris is way too easywhen played this way
Tuesday, October 2, 12
JVM & Its Languages
4
t1995
Scala,
Groovy, Closure, K
otlin...
Java
2012
What'spossible?
Tuesday, October 2, 12
About Me
• Project lead of Kotlin ➡ at JetBrains since 2010
• EG member of JSR-335➡ Project Lambda
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(not (RICH HICKEY))
Tuesday, October 2, 12
Kotlin
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Modern Language for Industry
• Static typing
• Readability
• Tool support
• Interoperability
• Smart compiler
➡ Less boilerplate
• Flexible abstractions
➡ Powerful libraries
Tuesday, October 2, 12
Outline
• Extensions
• Bridges of All Sorts
• Types: Collections and Nulls
• Dreams... (maybe)
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Tuesday, October 2, 12
Extensions
• Live Demo➡ Extension syntax
➡ How it is compiled
➡ Multiple files in a package
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Tuesday, October 2, 12
Bridges
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Tuesday, October 2, 12
Bridges for Generics
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(Lj/l/Object;)Lj/l/Object;
(I)I
(Lj/l/Object;)Lj/l/Object;
over
ride
s
"synthetic bridge method" (JLS)
Tuesday, October 2, 12
Kotlin Brides & Primitives
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1
foo(t: T) = t
1
1
foo(t: Int) = t
1
Java&
KotlinKotlin
Tuesday, October 2, 12
Default Arguments
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Tuesday, October 2, 12
Masks for Defaults
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foo(a, b) foo(a, b, mask: Int)if (mask & 1) a = 0if (mask & 2) b = 0foo(a, b)
Tuesday, October 2, 12
Traits: Code in Interfaces
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class Trait$Impl { static foo()V { println("Hi") }}
Tuesday, October 2, 12
Trait Hierarchy
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T1
T2
C
foo() { println() }
foo() { T2$Impl.foo()}
foo() { T1$Impl.foo() }
Tuesday, October 2, 12
Summary
• Sometimes you need just one more method...
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Tuesday, October 2, 12
CollectionsHow Data-Compatible is Your Language?
Tuesday, October 2, 12
Collections & Variance
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Java:
Kotlin:
Tuesday, October 2, 12
Kotlin's Collections
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Tuesday, October 2, 12
Declaration-Site Variance
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Tuesday, October 2, 12
Translation
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Øjava.util.List
Tuesday, October 2, 12
Translation: Inheritance
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Tuesday, October 2, 12
Translation: Variance
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Tuesday, October 2, 12
Calling Java From Kotlin
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Tuesday, October 2, 12
Summary
• Kotlin's collections➡ Better than Java's
➡ Still Compatible
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Tuesday, October 2, 12
Nullable Types
Tuesday, October 2, 12
Demo
• Kotlin is null-safe
• Java code can be annotated for safe access
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Tuesday, October 2, 12
Talk Summary
• Languages are about tradeoffs
• Kotlin is cool :)
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Tuesday, 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
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Tuesday, October 2, 12
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