1. Kotlin: How Things Work
Practical Aspects of JVM Language
Implementation
Andrey Breslav
Tuesday, October 2, 12

2. Why you should care
• Language is an abstraction
➡ thus it leaks
abstraction
• When something weird happens
➡ you may need to "see through the Matrix"
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3. tetris is way too easy
when played this way
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4. JVM & Its Languages
What's
i n...
otl
e , K possible?
sur
Clo
vy,
G roo
,
Sc ala
Java
t
1995 2012
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5. About Me
• Project lead of Kotlin
➡ at JetBrains since 2010
(not
(RICH HICKEY))
• EG member of JSR-335
➡ Project Lambda
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6. Kotlin
Modern Language for Industry
• Smart compiler • Static typing
➡ Less boilerplate • Readability
• Flexible abstractions • Tool support
➡ Powerful libraries • Interoperability
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7. Outline
• Extensions
• Bridges of All Sorts
• Types: Collections and Nulls
• Dreams... (maybe)
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8. Extensions
• Live Demo
➡ Extension syntax
➡ How it is compiled
➡ Multiple files in a package
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9. Bridges
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10. Bridges for Generics
(Lj/l/Object;)Lj/l/Object;
overrides
(I)I
(Lj/l/Object;)Lj/l/Object;
"synthetic bridge method" (JLS)
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11. Kotlin Brides & Primitives
Java 1 1
& Kotlin
Kotlin
foo(t: T) = t foo(t: Int) = t
1 1
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12. Default Arguments
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13. Masks for Defaults
foo(a, b) foo(a, b, mask: Int)
if (mask & 1)
a = 0
if (mask & 2)
b = 0
foo(a, b)
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14. Traits: Code in Interfaces
class Trait$Impl {
static foo()V {
println("Hi")
}
}
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15. Trait Hierarchy
T1 foo() { println() }
T2 foo() { T1$Impl.foo() }
C foo() {
T2$Impl.foo()
}
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16. Summary
• Sometimes you need just one more
method...
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17. Collections
How Data-Compatible is Your Language?
Tuesday, October 2, 12

18. Collections & Variance
Java:
Kotlin:
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19. Kotlin's Collections
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20. Declaration-Site Variance
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21. Translation
Ø
java.util.List
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22. Translation: Inheritance
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23. Translation: Variance
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24. Calling Java From Kotlin
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25. Summary
• Kotlin's collections
➡ Better than Java's
➡ Still Compatible
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26. Nullable Types
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27. Demo
• Kotlin is null-safe
• Java code can be annotated for safe
access
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28. Talk Summary
• Languages are about tradeoffs
• Kotlin is cool :)
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29. 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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