1. Kotlin Bytecode Generation
and
Runtime Performance
Dmitry Jemerov
Dmitry Jemerov, 11-13 May 2016

2. What is Kotlin

3. What is Kotlin

4. What is Kotlin
• Statically typed programming language for JVM, Android and the
browser
• Pragmatic, safe, concise, seamless Java interop

5. What is Kotlin
• Statically typed programming language for the JVM, Android and
the browser
• Pragmatic, safe, concise, seamless Java interop

6. Compiling a mixed project
*.java
kotlinc
*.kt
*.class
javac *.class
*.jar

7. Metadata
@Metadata(
mv = {1, 1, 1},
bv = {1, 0, 0},
k = 1,
d1 = {"u0000"nu0002u0018u0002nu0002u0018u0002nu0002bu0002nu0002u0010bnu0000n
u0002u0010u0002nu0002bu0005nu0002u0018u0002nu0002bu0002bu0017u0018u00002u00020u0001Bu0005¢
u0006u0002u0010u0002Jbu0010u0003u001au00020u0004Hu0007Jbu0010u0005u001au00020u0006Hu0007Jb
u0010u0007u001au00020u0004Hu0007Jbu0010bu001au00020u0004Hu0007J!u0010tu001au0002Hn"u0004b
u0000u0010n2fu0010u000bu001abu0012u0004u0012u0002Hn0fHu0002¢u0006u0002u0010r¨u0006u000e"},
d2 = {"Lorg/jetbrains/LambdaBenchmark;", "Lorg/jetbrains/SizedBenchmark;", "()V", "capturingLambda", "",
"init", "", "mutatingLambda", "noncapturingLambda", "runLambda", "T", "x", "Lkotlin/Function0;", "(Lkotlin/jvm/
functions/Function0;)Ljava/lang/Object;", "production sources for module kotlin-benchmarks"}
)
public class LambdaBenchmark extends SizedBenchmark
{ … }

8. Working with metadata
class A {
fun foo(): String? = null
fun bar(): String = ""
}
fun main(args: Array<String>) {
println(A::class.functions.filter {
it.returnType.isMarkedNullable
})
}

9. File-level functions
// Data.kt
fun foo() {
}
public final class DataKt {
public static void foo() {
}
}

10. @JvmName
@file:JvmName("FooUtils")
fun foo() {
}
public final class FooUtils {
public static final void foo() {
}
}

11. Primary constructors
class A(val x: Int) {
}
public final class A {
private final int x;
public final int getX() {
return this.x;
}
public A(int x) {
this.x = x;
}
}

12. Data classes
data class A(val x: Int) {
}
public final class A {
…
public String toString() {
return "A(x=" + this.x + ")";
}
public int hashCode() {
return this.x;
}
public boolean equals(Object o) {
…
}
}

13. Properties
class A {
var x: String? = null
}
public final class A {
@Nullable
private String x;
@Nullable
public final String getX() {
return this.x;
}
public final void setX(
@Nullable String x) {
this.x = x;
}
}

14. @JvmField
class A {
@JvmField var x: String? = null
}
public final class A {
@JvmField
@Nullable
public String x;
}

15. Not-null types
class A {
fun x(s: String) {
println(s)
}
private fun y(s: String) {
println(s)
}
}
public final class A {
public final void x(@NotNull String s) {
Intrinsics.
checkParameterIsNotNull(s, "s");
System.out.println(s);
}
private final void y(String s) {
System.out.println(s);
}
}

16. Parameter null checks
1 parameter
8 parameters
ns
0 2,25 4,5 6,75 9
Without @NotNull With @NotNull

17. Extension functions
class A(val i: Int)
fun A.foo(): Int {
return i
}
fun useFoo() {
A(1).foo()
}
public final class ExtFunKt {
public static final void foo(
@NotNull A $receiver) {
return $receiver.getI();
}
}
public static final void useFoo() {
foo(new A(1));
}

18. Interface methods
interface I {
fun foo(): Int {
return 42
}
}
class C : I {
}
public interface I {
int foo();
public static final class
DefaultImpls {
public static int foo(I $this) {
return 42;
}
}
}
public final class C implements I {
public void foo() {
I.DefaultImpls.foo(this);
}
}

19. Interface methods: Evolution
interface I {
fun foo(): Int {
return 42
}
fun bar(): Int {
return 239
}
}
// -- separate compilation ——————
class C : I {
}
public interface I {
int foo();
int bar();
public static final class
DefaultImpls { … }
}
// -- separate compilation ——————
public final class C implements I {
public void foo() {
I.DefaultImpls.foo(this);
}
}

20. Default Arguments
fun foo(x: Int = 42) {
println(x)
}
fun bar() {
foo()
}
public static final void foo(int x) {
System.out.println(x);
}
public static void foo$default(
int x, int mask, …) {
if ((mask & 1) != 0) {
x = 42;
}
foo(x);
}
public static final void bar() {
foo$default(0, 1, …);
}

21. Default Arguments
1 parameter
8 parameters
ns
0 3,75 7,5 11,25 15
Without default values With default values

22. @JvmOverloads
@JvmOverloads
fun foo(x: Int = 42) {
}
public static final void foo(int x)
{
}
public static void foo$default(
int x, int mask, …) { … }
public static void foo() {
foo$default(0, 1, …);
}

23. Lambdas: Functional types
fun <T> runLambda(x: () -> T): T =
x()
private static final
Object runLambda(Function0 x) {
return x.invoke();
}
package kotlin.jvm.functions
/** A function that takes 0 arguments. */
public interface Function0<out R> : Function<R> {
/** Invokes the function. */
public operator fun invoke(): R
}

24. Lambdas: Noncapturing
var value = 0
fun noncapLambda(): Int
= runLambda { value }
final class LB$noncapLambda$1
extends Lambda implements Function0 {
public static final LB$noncapLambda$1
INSTANCE = new LB$noncapLambda$1();
public final int invoke() {
return LambdaBenchmarkKt.getValue();
}
}
public static int noncapLambda() {
return ((Number)runLambda(
LB$noncapLambda$1.INSTANCE)
).intValue();
}

25. Lambdas: Capturing
fun capturingLambda(v: Int): Int
= runLambda { v }
public static int
capturingLambda(int value) {
return ((Number)RL.runLambda(
new Function0(0) {
public final int invoke() {
return value;
}
})
).intValue();

26. Lambdas: Capture and mutate
fun mutatingLambda(): Int {
var x = 0
runLambda { x++ }
return x
}
public static int mutatingLambda()
{
final IntRef x = new IntRef();
x.element = 0;
RL.runLambda(new Function0(0) {
public final int invoke() {
int var1 = x.element++;
return var1;
}
});
return x.element;
}
public static final class IntRef {
public volatile int element;
@Override
public String toString() {
return String.valueOf(element);
}
}

27. Lambdas
Noncapturing
Capturing
Mutating
ns
0 45 90 135 180
Java Kotlin

28. Lambdas: inline
fun inlineLambda(x: Int): Int =
run { x }
public static int
inlineLambda(int x) {
return x;
}
/**
* Calls the specified function [block] and returns its result.
*/
public inline fun <R> run(block: () -> R): R = block()

29. Method References
private fun referenced() = 1
fun runReference() {
runLambda(::referenced)
}
final class MethodReferenceKt$runReference$1
extends FunctionReference implements Function0
{
public static final MethodReferenceKt
$runReference$1 INSTANCE = new
MethodReferenceKt$runReference$1();
public final int invoke() {
return MethodReferenceKt.access
$referenced();
}
public final KDeclarationContainer
getOwner() { … }
public final String getName() { … }
public final String getSignature() { … }
}

30. Loops: Range
fun rangeLoop() {
for (i in 1..10) {
println(i)
}
}
public static final void
rangeLoop() {
int i = 1;
byte var1 = 10;
if(i <= var1) {
while(true) {
System.out.println(i);
if(i == var1) {
break;
}
++i;
}
}
}

31. Loops: Array
fun arrayLoop(x: Array<String>) {
for (s in x) {
println(s)
}
}
public static void
arrayLoop(@NotNull String[] x) {
for(int var2 = 0;
var2 < x.length; ++var2) {
String s = x[var2];
System.out.println(s);
}
}

32. Loops: List
fun listLoop(x: List<String>) {
for (s in x) {
println(s)
}
}
public static final void
listLoop(@NotNull List x) {
Iterator var2 = x.iterator();
while(var2.hasNext()) {
String s =
(String)var2.next();
System.out.println(s);
}
}

33. Loops
Range
Array
ArrayList
ns
0 27,5 55 82,5 110
Java Kotlin

34. When: Table lookup
fun tableWhen(x: Int): String =
when(x) {
0 -> "zero"
1 -> "one"
else -> "many"
}
public static String tableWhen(int x)
{
String var10000;
switch(x) {
case 0:
var10000 = "zero";
break;
case 1:
var10000 = "one";
break;
default:
var10000 = "many";
}
return var10000;
}

35. When: Constants
val ZERO = 0
val ONE = 1
fun constWhen(x: Int): String =
when(x) {
ZERO -> "zero"
ONE -> "one"
else -> "many"
}
public static String constWhen(
int x) {
return x == ZERO ? “zero"
: (x == ONE ? “one" : "many");
}

36. When: enum
enum class NumberValue {
ZERO, ONE, MANY
}
fun enumWhen(x: NumberValue):
String = when(x) {
NumberValue.ZERO -> "zero"
NumberValue.ONE -> "one"
else -> "many"
}
public static String
enumWhen(@NotNull NumberValue x) {
String var10000;
switch(WhenEnumKt$WhenMappings.
$EnumSwitchMapping$0[x.ordinal()]) {
case 1:
var10000 = "zero";
break;
case 2:
var10000 = "one";
break;
default:
var10000 = "many";
}
return var10000;
}

37. When
Lookup
Compare
Enum
ns
0 5,5 11 16,5 22
Java Kotlin

38. Summary
• Kotlin allows writing code which is easy to use from Java
• Performance in most scenarios is on par with Java
• Inline functions 👍
• Measure the performance of your code, not micro-examples

39. https://www.manning.com/books/kotlin-in-action

40. Q&A
yole@jetbrains.com
@intelliyole