Inline functions in Kotlin

Presentation I gave in the Kotlin Conf event in Lima, 2019.

Transcript

1. Jose Flavio Quispe Irrazábal Software Engineer @jflavio11 Inline functions in Kotlin A first approach Android Dev Perú
2. In this presentation • Anonymous classes, functions and lambda expressions. • Functions in Kotlin. • Inline functions. • What is the Java Bytecode? • Things to keep in mind: return statement. • Extra
3. The beginning
4. Anonymous classes, anonymous functions and lambda expressions • Anonymous classes → create entities from an interface without creating an implementation class. Kotlin Everywhere
5. Anonymous classes, anonymous functions and lambda expressions • Lambdas → reference anonymous functions (or without name). Replace the use of anonymous classes. Kotlin Everywhere
6. High Order Functions Functions in Kotlin are first-class: • They can be passed as parameters • They can be stored in variables • They can be returned from another high-order function Kotlin Everywhere
7. High Order Functions Kotlin Everywhere But an object is created every time you assigned to a variable or pass it as a parameter to another function
8. Simple example Kotlin Everywhere fun myFilter(list: List, funcion: (Double, Double) -> Boolean): List myFilter(teachersList) { ratingYearOne, reatingYearTwo -> (ratingYearOne + reatingYearTwo)/2 >= 7.0 } myFilter(teachersList, new Funcion() { @Override public boolean function(Double ratingYearOne, reatingYearTwo) { return (ratingYearOne + reatingYearTwo)/2 >= 7.0 ; } });
9. Inline functions
10. Inline functions • Using inline keyword, we tell the compiler to copy functions and parameters to the call site. • In normal functions its code is set in memory. Everytime it is tried to be invoked, parameters are added to the memory stack and then it is invoked. Kotlin Everywhere
11. Inline functions Kotlin Everywhere
12. Decompiled bytecode (without inline)
14. Bytecode and JVM Languages?
15. JVM Languages • Every language that runs on the JVM: Scala, Java, Kotlin, Jython, etc. • Compile to Java Bytecode. Kotlin Everywhere
16. Bytecode • Instruction set of the JVM. • Then, the JVM is independent of any OS. Kotlin Everywhere
17. Bytecode Kotlin Everywhere
18. Decompiled bytecode (without inline)
19. Inline functions Kotlin Everywhere
21. Decompiled bytecode (using inline)
22. Inline functions Kotlin Everywhere
24. Inline functions • Using inline keyword, we tell the compiler to copy functions and parameters to the call site. Kotlin Everywhere
25. Inline functions To Keep in mind • Normal “return” statement is not allowed inside a lambda, we must use a label → local return. • Above behavior, is similar in anonymous functions. Kotlin Everywhere
26. Log Found Bart Did we find Bart? End of findStudent
27. Inline functions To Keep in mind • “return” returns the nearest function declaration. • In lambdas, the enclosing function is where the nearest fun declaration is. Kotlin Everywhere
28. Inline functions return statement Kotlin Everywhere
29. return statement: decompiled bytecode (without inline) Kotlin Everywhere return ??
30. Inline functions Kotlin Everywhere Log Found Bart
31. Conclusions
32. Inline functions • Inline functions can reduce memory overhead (and time execution). Kotlin Everywhere • Increase resulting bytecode. • We should avoid them in large code logic. • TODOs (read about) : ◦ no inline ◦ crossinline ◦ refied • We should keep in mind of return statement.
33. Extra
35. Kotlin Everywhere Tested in a Macbook Pro early 2015 - i5 - 8GB RAM 1 2 3 4 5 6 7 8 9 10 Average 8432 7354 7840 6846 7633 7139 7113 8085 9147 6873 7646.2 ms Time comparison • Using inline keyword • Normal lambda 1 2 3 4 5 6 7 8 9 10 Average 15799 16067 16293 16293 15606 15216 15292 15667 15695 19755 16168.3 ms
36. Use of inline functions
37. Thank You! Jose Flavio Quispe Irrazábal Software Engineer @jflavio11 Android Dev Perú