TimePad event: https://jugru.timepad.ru/event/296642/ Habrahbr announcement: https://habrahabr.ru/company/jugru/blog/277871/ Videos: - https://www.youtube.com/watch?v=HWyd1gYMkl0 - https://www.youtube.com/watch?v=LWFx4QWrTyo

1. Andrey Breslav

2. http://kotlinlang.org

3. JetBrains

4. • Pragmatic language for industry
– Started in 2010
– Open Source
– 1.0 Released in Feb, 2016
• For JVM, Android, and JavaScript
– Interoperability: 100%
• Try online: https://try.kotl.in

5. bytecode
Kotlin

6. Technicalities
• Few compiler optimizations
– inlning as a language feature
• Compiler intergated into the IDE
• Incrementality

8. Requirements
• Statically typed
• “Toolable” (is this a word at all?)
• Interoperable (yes, C++ has been there!)
• Learnable (“democratic”)

9. Comparing to others

11. Over 500K LOC of Kotlin:
IntelliJ IDEA
Rider (C# IDE)
YouTrack
JetBrains Account
(and more)

13. In Open-Source Projects, Kotlin itself excluded

14. In Open-Source Projects, Kotlin itself excluded

15. IDE
Compiler
(Incremental)
Build System

16. Java
*.kt *.java
compiler
Javacompiler

19. “Billion dollar mistake”
— Sir C. A. R. Hoare

20. Java String s = null;
s.length();
Errors At Runtime
Kotlin val s: String
s.length()
val s: String? = null
s.length()
Errors At Compile Time
= null
Nullable
type

21. Check and use val s: String? = …
if (s != null) {
s.length()
}
Check and exit if (s == null) return
s.length()
Rock’n’Roll s?.length()
s!!.length()
(s ?: “…”).length()

22. Kotlin is good with nulls

23. What about
Java?

24. Java (as seen from Kotlin)
public class JavaClass {
public String foo(List<String> l) {…}
}
String
String?
List<String>
List<String?>
List<String>?
List<String?>?
Safest!

25. Java Interop: All Nullable
javaValue.toString().length() + 1
javaValue?.toString()?.length()!! + 1
val l: List<String> = javaValue?.getList()!!
ArrayList<String?>

26. Your safest
option doesn’t
work!

27. Annotations
public class JavaClass {
@NotNull
public String foo(@NotNull List<String> l) {…}
}
String
String?
List<String>
List<String?>
List<String>?
List<String?>?

28. Annotations are
cumbersome
AND
don’t really help!

29. Pick Two
• Null-safety
• Convenience
• Java Interop
Platform Types!
Thanks to
Dr. Ross Tate of

30. Java: Platform Types
public class JavaClass {
public String foo(Bar<String> l) {…}
}
String! Bar<String!>!
Platform Type

31. Dereferencing Platform Values
s: String s: String? s: String!
s.length() s.length() s.length()
s?.length() s?.length() s?.length()
s!!.length() s!!.length() s!!.length()
NPE

32. Assignability
String String?
String!
Platform Type
NPE

33. Some Notes
• Platform Types are Not Denotable!
– String! is notation, not syntax
• Pure Kotlin is Null-Safe
• Kotlin+Java is as safe as Java
• Annotations Still Applicable
– @NotNull String in Java becomes String in Kotlin
• Dynamic Type for JavaScript Interop
– JS is even unsafer than Java

34. Nullable types: Summary
Cost
• More Complexity
• Less Null-Safety
Benefit
• Smooth Interop

35. http://kotlinlang.org

36. Images Used
• http://blogs.msdn.com/cfs-
filesystemfile.ashx/__key/communityserver-blogs-components-
weblogfiles/00-00-01-32-02-
metablogapi/8054.image_5F00_thumb_5F00_35C6E986.png
• http://www.complete-coherence.com/wp-
content/uploads/2015/06/Is-business-rational-or-emotional.jpg
• http://www.mightyheaton.com/wp-content/uploads/2012/05/33-
1024x908.jpg
• https://openclipart.org/image/2400px/svg_to_png/97543/text-file-
icon.png
• http://fileinfo.com/img/icons/files/128/class-737.png
• http://1.bp.blogspot.com/-
UK5uEhDELUA/T9duhHrDeII/AAAAAAAAB20/nKpYXYhqub4/s1600/
application-x-jar%5B1%5D.png