Deep Dive Kotlin :
du Hello World au ByteCode

Speakers

Emmanuel Vinas

Expert Android & Java

@emmanuelvinas emmanuel@monkeypatch.io

Igor Laborie

Expert Web & Java

@ilaborie igor@monkeypatch.io

Roadmap

Introduction
ByteCode Java ?
Introduction Kotlin
Les bases
null-safety
Les types
Les fonctions
Les lambdas
Les classes
Pause
ByteCode Android
Autres structures
Extensions de fonctions
Les collections
Les delegates
inline
Coroutines
Conclusion

ByteCode Java ?

javac

Java compiler

HelloWorld.java

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello RivieraDev");
    }
}

javac HelloWorld.java

Java ByteCode binary

hexdump -C HelloWorld.class

00000000  ca fe ba be 00 00 00 34  00 1d 0a 00 06 00 0f 09  |.......4........|
00000010  00 10 00 11 08 00 12 0a  00 13 00 14 07 00 15 07  |................|
00000020  00 16 01 00 06 3c 69 6e  69 74 3e 01 00 03 28 29  |.....<init>...()|
00000030  56 01 00 04 43 6f 64 65  01 00 0f 4c 69 6e 65 4e  |V...Code...LineN|
00000040  75 6d 62 65 72 54 61 62  6c 65 01 00 04 6d 61 69  |umberTable...mai|
00000050  6e 01 00 16 28 5b 4c 6a  61 76 61 2f 6c 61 6e 67  |n...([Ljava/lang|
00000060  2f 53 74 72 69 6e 67 3b  29 56 01 00 0a 53 6f 75  |/String;)V...Sou|
00000070  72 63 65 46 69 6c 65 01  00 0f 48 65 6c 6c 6f 57  |rceFile...HelloW|
00000080  6f 72 6c 64 2e 6a 61 76  61 0c 00 07 00 08 07 00  |orld.java.......|
00000090  17 0c 00 18 00 19 01 00  0c 48 65 6c 6c 6f 20 44  |.........Hello D|
000000a0  65 76 6f 78 78 07 00 1a  0c 00 1b 00 1c 01 00 19  |evoxx...........|
000000b0  5f 30 30 5f 68 65 6c 6c  6f 77 6f 72 6c 64 2f 48  |_00_helloworld/H|
000000c0  65 6c 6c 6f 57 6f 72 6c  64 01 00 10 6a 61 76 61  |elloWorld...java|
000000d0  2f 6c 61 6e 67 2f 4f 62  6a 65 63 74 01 00 10 6a  |/lang/Object...j|
000000e0  61 76 61 2f 6c 61 6e 67  2f 53 79 73 74 65 6d 01  |ava/lang/System.|
000000f0  00 03 6f 75 74 01 00 15  4c 6a 61 76 61 2f 69 6f  |..out...Ljava/io|
00000100  2f 50 72 69 6e 74 53 74  72 65 61 6d 3b 01 00 13  |/PrintStream;...|
00000110  6a 61 76 61 2f 69 6f 2f  50 72 69 6e 74 53 74 72  |java/io/PrintStr|
00000120  65 61 6d 01 00 07 70 72  69 6e 74 6c 6e 01 00 15  |eam...println...|
00000130  28 4c 6a 61 76 61 2f 6c  61 6e 67 2f 53 74 72 69  |(Ljava/lang/Stri|
00000140  6e 67 3b 29 56 00 21 00  05 00 06 00 00 00 00 00  |ng;)V.!.........|
00000150  02 00 01 00 07 00 08 00  01 00 09 00 00 00 1d 00  |................|
00000160  01 00 01 00 00 00 05 2a  b7 00 01 b1 00 00 00 01  |.......*........|
00000170  00 0a 00 00 00 06 00 01  00 00 00 03 00 09 00 0b  |................|
00000180  00 0c 00 01 00 09 00 00  00 25 00 02 00 01 00 00  |.........%......|
00000190  00 09 b2 00 02 12 03 b6  00 04 b1 00 00 00 01 00  |................|
000001a0  0a 00 00 00 0a 00 02 00  00 00 06 00 08 00 07 00  |................|
000001b0  01 00 0d 00 00 00 02 00  0e                       |.........|
000001b9

Explorons le ByteCode

javap -c HelloWorld.class

Compiled from "HelloWorld.java"
public class _00_helloworld.HelloWorld {
  public _00_helloworld.HelloWorld();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: ldc           #3                  // String Hello RivieraDev
       5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
       8: return
}

À propos du ByteCode

Environ 200 opérations possibles (maxi. 256 opscodes)
Préfixe pour le type d'opérations (i pour entier, d pour double, ...)
Manipulation de la pile, des variables locales (iconst_0, istore, iload, ...)
Contrôle du flux des instructions (if_icmpgt, goto, ...)
Arithmétique et conversion de type (iadd, iinc, i2d, ...)
Manipulation d'objets (invokevirtual, invokedynamic, ...)
Autres (athrow, ...)

Jouons un peu

Liens

Soyez curieux, regardez comment ça marche avec javap -c !

Introduction Kotlin

Historique

2011 - 2015

Dévoilé par JetBrains
2016

v1.0

Support annoncé par Spring
2017

v1.1 : coroutines, JS, ...

Support par Google

v1.2 : multiplatform
2018

v1.3

Coroutine stable

Kotlin Native beta

Kotlin Foundation
2019

corountine-flow

v1.4 ?

???
...

Cibles

JVM et Android

JavaScript

Native avec LLVM

HelloWorld.kt

fun main() {
    println("Hello RivieraDev")
}

kotlinc HelloWorld.kt

kotlinc

hexdump

00000000  ca fe ba be 00 00 00 32  00 2b 01 00 0c 48 65 6c  |.......2.+...Hel|
00000010  6c 6f 57 6f 72 6c 64 4b  74 07 00 01 01 00 10 6a  |loWorldKt......j|
00000020  61 76 61 2f 6c 61 6e 67  2f 4f 62 6a 65 63 74 07  |ava/lang/Object.|
00000030  00 03 01 00 04 6d 61 69  6e 01 00 03 28 29 56 01  |.....main...()V.|
00000040  00 16 28 5b 4c 6a 61 76  61 2f 6c 61 6e 67 2f 53  |..([Ljava/lang/S|
00000050  74 72 69 6e 67 3b 29 56  0c 00 05 00 06 0a 00 02  |tring;)V........|
00000060  00 08 01 00 10 48 65 6c  6c 6f 20 52 69 76 69 65  |.....Hello Rivie|
00000070  72 61 44 65 76 08 00 0a  01 00 10 6a 61 76 61 2f  |raDev......java/|
00000080  6c 61 6e 67 2f 53 79 73  74 65 6d 07 00 0c 01 00  |lang/System.....|
00000090  03 6f 75 74 01 00 15 4c  6a 61 76 61 2f 69 6f 2f  |.out...Ljava/io/|
000000a0  50 72 69 6e 74 53 74 72  65 61 6d 3b 0c 00 0e 00  |PrintStream;....|
000000b0  0f 09 00 0d 00 10 01 00  13 6a 61 76 61 2f 69 6f  |.........java/io|
000000c0  2f 50 72 69 6e 74 53 74  72 65 61 6d 07 00 12 01  |/PrintStream....|
000000d0  00 07 70 72 69 6e 74 6c  6e 01 00 15 28 4c 6a 61  |..println...(Lja|
000000e0  76 61 2f 6c 61 6e 67 2f  4f 62 6a 65 63 74 3b 29  |va/lang/Object;)|
000000f0  56 0c 00 14 00 15 0a 00  13 00 16 01 00 11 4c 6b  |V.............Lk|
00000100  6f 74 6c 69 6e 2f 4d 65  74 61 64 61 74 61 3b 01  |otlin/Metadata;.|
00000110  00 02 6d 76 03 00 00 00  01 03 00 00 00 0f 01 00  |..mv............|
00000120  02 62 76 03 00 00 00 00  03 00 00 00 03 01 00 01  |.bv.............|
00000130  6b 03 00 00 00 02 01 00  02 64 31 01 00 13 c0 80  |k........d1.....|
00000140  06 0a c0 80 0a 02 10 02  1a 06 10 c0 80 1a 02 30  |...............0|
00000150  01 01 00 02 64 32 01 00  00 01 00 0d 48 65 6c 6c  |....d2......Hell|
00000160  6f 57 6f 72 6c 64 2e 6b  74 01 00 04 43 6f 64 65  |oWorld.kt...Code|
00000170  01 00 0f 4c 69 6e 65 4e  75 6d 62 65 72 54 61 62  |...LineNumberTab|
00000180  6c 65 01 00 0a 53 6f 75  72 63 65 46 69 6c 65 01  |le...SourceFile.|
00000190  00 14 53 6f 75 72 63 65  44 65 62 75 67 45 78 74  |..SourceDebugExt|
000001a0  65 6e 73 69 6f 6e 01 00  19 52 75 6e 74 69 6d 65  |ension...Runtime|
000001b0  56 69 73 69 62 6c 65 41  6e 6e 6f 74 61 74 69 6f  |VisibleAnnotatio|
000001c0  6e 73 00 31 00 02 00 04  00 00 00 00 00 02 00 19  |ns.1............|
000001d0  00 05 00 06 00 01 00 26  00 00 00 29 00 02 00 02  |.......&...)....|
000001e0  00 00 00 0d 12 0b 4b 03  3c b2 00 11 2a b6 00 17  |......K.<...*...|
000001f0  b1 00 00 00 01 00 27 00  00 00 0a 00 02 00 00 00  |......'.........|
00000200  02 00 0c 00 03 10 09 00  05 00 07 00 01 00 26 00  |..............&.|
00000210  00 00 10 00 00 00 01 00  00 00 04 b8 00 09 b1 00  |................|
00000220  00 00 00 00 03 00 28 00  00 00 02 00 25 00 29 00  |......(.....%.).|
00000230  00 00 54 53 4d 41 50 0a  48 65 6c 6c 6f 57 6f 72  |..TSMAP.HelloWor|
00000240  6c 64 2e 6b 74 0a 4b 6f  74 6c 69 6e 0a 2a 53 20  |ld.kt.Kotlin.*S |
00000250  4b 6f 74 6c 69 6e 0a 2a  46 0a 2b 20 31 20 48 65  |Kotlin.*F.+ 1 He|
00000260  6c 6c 6f 57 6f 72 6c 64  2e 6b 74 0a 48 65 6c 6c  |lloWorld.kt.Hell|
00000270  6f 57 6f 72 6c 64 4b 74  0a 2a 4c 0a 31 23 31 2c  |oWorldKt.*L.1#1,|
00000280  34 3a 31 0a 2a 45 0a 00  2a 00 00 00 3a 00 01 00  |4:1.*E..*...:...|
00000290  18 00 05 00 19 5b 00 03  49 00 1a 49 00 1a 49 00  |.....[..I..I..I.|
000002a0  1b 00 1c 5b 00 03 49 00  1a 49 00 1d 49 00 1e 00  |...[..I..I..I...|
000002b0  1f 49 00 20 00 21 5b 00  01 73 00 22 00 23 5b 00  |.I. .![..s.".#[.|
000002c0  02 73 00 05 73 00 24                              |.s..s.$|
000002c7

Java ByteCode

Compiled from "HelloWorld.kt"
public final class HelloWorldKt {
  public static final void main();
    Code:
       0: ldc           #11                 // String Hello RivieraDev
       2: astore_0
       3: iconst_0
       4: istore_1
       5: getstatic     #17                 // Field java/lang/System.out:Ljava/io/PrintStream;
       8: aload_0
       9: invokevirtual #23                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      12: return

  public static void main(java.lang.String[]);
    Code:
       0: invokestatic  #9                  // Method main:()V
       3: return
}

HelloWorld-java

import kotlin.Metadata;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\b\n\u0000\n\u0002\u0010\u0002\n\u0000\u001a\u0006\u0010\u0000\u001a\u00020\u0001¨\u0006\u0002"},
        d2 = {"main", "", "kotlinDee"}
)
public final class HelloWorldKt {
   public static final void main() {
      String var0 = "Hello RivieraDev";
      boolean var1 = false;
      System.out.println(var0);
   }

   // $FF: synthetic method
   public static void main(String[] var0) {
      main();
   }
}

Bilan HelloWorld.kt

Kotlin ajoute du contenu
du coup, on a besoin de JARs en plus

Taille des JAR
	jar	version	taille
kotlin-stdlib	kotlin-stdlib	1.3.31	1.3M
kotlin-stdlib-jdk7	kotlin-stdlib-jdk7	1.3.31	3.1k
kotlin-stdlib-jdk8	kotlin-stdlib-jdk8	1.3.31	13k
kotlin-reflect	kotlin-reflect	1.3.31	2.8M
lombok	lombok	1.18.6	1.7M
spring-core	spring-core	5.1.6	1.3M

Les bases

val-var.kt

var x: Int = 10
val y: Int = 3
x += 4
// y += 4 <== 💣 Compilation Error

println(x * y) // 42

string-template.kt

fun greeting(who: Someone) {
    println("Hello $who!")
    println("Hello ${who.firstName} ${who.lastName}!")
    println("""
        multi
        line "$who"
        string""".trimIndent())
}

string-template.java

import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import kotlin.text.StringsKt;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u000e\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u001a\u000e\u0010\u0000\u001a\u00020\u00012\u0006\u0010\u0002\u001a\u00020\u0003¨\u0006\u0004"},
        d2 = {"greeting", "", "who", "LSomeone;", "kotlinDee"}
)
public final class GreetingKt {
   public static final void greeting(@NotNull Someone who) {
      Intrinsics.checkParameterIsNotNull(who, "who");
      String var1 = "Hello " + who + '!';
      boolean var2 = false;
      System.out.println(var1);
      var1 = "Hello " + who.getFirstName() + ' ' + who.getLastName() + '!';
      var2 = false;
      System.out.println(var1);
      var1 = StringsKt.trimIndent("\n        multi\n        line \"" + who + "\"\n        string");
      var2 = false;
      System.out.println(var1);
   }
}

ByteCode de string-template

Compiled from "greeting.kt"
public final class GreetingKt {
  public static final void greeting(Someone);
    Code:
       0: aload_0
       1: ldc           #9                  // String who
       3: invokestatic  #15                 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
       6: new           #17                 // class java/lang/StringBuilder
       9: dup
      10: invokespecial #21                 // Method java/lang/StringBuilder."<init>":()V
      13: ldc           #23                 // String Hello
      15: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      18: aload_0
      19: invokevirtual #30                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
      22: bipush        33
      24: invokevirtual #33                 // Method java/lang/StringBuilder.append:(C)Ljava/lang/StringBuilder;
      27: invokevirtual #37                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      30: astore_1
      31: iconst_0
      32: istore_2
      33: getstatic     #43                 // Field java/lang/System.out:Ljava/io/PrintStream;
      36: aload_1
      37: invokevirtual #49                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      40: new           #17                 // class java/lang/StringBuilder
      43: dup
      44: invokespecial #21                 // Method java/lang/StringBuilder."<init>":()V
      47: ldc           #23                 // String Hello
      49: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      52: aload_0
      53: invokevirtual #54                 // Method Someone.getFirstName:()Ljava/lang/String;
      56: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      59: bipush        32
      61: invokevirtual #33                 // Method java/lang/StringBuilder.append:(C)Ljava/lang/StringBuilder;
      64: aload_0
      65: invokevirtual #57                 // Method Someone.getLastName:()Ljava/lang/String;
      68: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      71: bipush        33
      73: invokevirtual #33                 // Method java/lang/StringBuilder.append:(C)Ljava/lang/StringBuilder;
      76: invokevirtual #37                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      79: astore_1
      80: iconst_0
      81: istore_2
      82: getstatic     #43                 // Field java/lang/System.out:Ljava/io/PrintStream;
      85: aload_1
      86: invokevirtual #49                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      89: new           #17                 // class java/lang/StringBuilder
      92: dup
      93: invokespecial #21                 // Method java/lang/StringBuilder."<init>":()V
      96: ldc           #59                 // String \n        multi\n        line \"
      98: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
     101: aload_0
     102: invokevirtual #30                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
     105: ldc           #61                 // String \"\n        string
     107: invokevirtual #27                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
     110: invokevirtual #37                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
     113: invokestatic  #67                 // Method kotlin/text/StringsKt.trimIndent:(Ljava/lang/String;)Ljava/lang/String;
     116: astore_1
     117: iconst_0
     118: istore_2
     119: getstatic     #43                 // Field java/lang/System.out:Ljava/io/PrintStream;
     122: aload_1
     123: invokevirtual #49                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
     126: return
}

numeric.kt

val anInt = 42  // type inference: Int
val aLong = 42L // type inference: Long
var aDouble: Double? = null

numeric.java

import kotlin.Metadata;
import org.jetbrains.annotations.Nullable;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u001a\n\u0000\n\u0002\u0010\u0006\n\u0002\b\u0006\n\u0002\u0010\t\n\u0002\b\u0003\n\u0002\u0010\b\n\u0002\b\u0003\"\u001e\u0010\u0000\u001a\u0004\u0018\u00010\u0001X\u0086\u000e¢\u0006\u0010\n\u0002\u0010\u0006\u001a\u0004\b\u0002\u0010\u0003\"\u0004\b\u0004\u0010\u0005\"\u0014\u0010\u0007\u001a\u00020\bX\u0086D¢\u0006\b\n\u0000\u001a\u0004\b\t\u0010\n\"\u0014\u0010\u000b\u001a\u00020\fX\u0086D¢\u0006\b\n\u0000\u001a\u0004\b\r\u0010\u000e¨\u0006\u000f"},
        d2 = {"aDouble", "", "getADouble", "()Ljava/lang/Double;", "setADouble", "(Ljava/lang/Double;)V", "Ljava/lang/Double;", "aLong", "", "getALong", "()J", "anInt", "", "getAnInt", "()I", "kotlinDee"}
)
public final class NumericKt {
   private static final int anInt = 42;
   private static final long aLong = 42L;
   @Nullable
   private static Double aDouble;

   public static final int getAnInt() {
      return anInt;
   }

   public static final long getALong() {
      return aLong;
   }

   @Nullable
   public static final Double getADouble() {
      return aDouble;
   }

   public static final void setADouble(@Nullable Double var0) {
      aDouble = var0;
   }
}

ByteCode de numeric

Compiled from "numeric.kt"
public final class NumericKt {
  public static final int getAnInt();
    Code:
       0: getstatic     #11                 // Field anInt:I
       3: ireturn

  public static final long getALong();
    Code:
       0: getstatic     #19                 // Field aLong:J
       3: lreturn

  public static final java.lang.Double getADouble();
    Code:
       0: getstatic     #26                 // Field aDouble:Ljava/lang/Double;
       3: areturn

  public static final void setADouble(java.lang.Double);
    Code:
       0: aload_0
       1: putstatic     #26                 // Field aDouble:Ljava/lang/Double;
       4: return

  static {};
    Code:
       0: bipush        42
       2: putstatic     #11                 // Field anInt:I
       5: ldc2_w        #14                 // long 42l
       8: putstatic     #19                 // Field aLong:J
      11: return
}

C'est simple

Plus de ; ^*
😍 String templating
😘 Plus de types primitifs (avant la compilation)
🧐 Inférence de type
🤝 On peut mélanger du code Java et Kotlin

null-safety

billion-dollar mistake

I call it my billion-dollar mistake. It was the invention of the null reference in 1965. [...] This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

⏤ Tony Hoare (C.A.R. Hoare)

Null References: The Billion Dollar Mistake

null-safety.kt

fun main() {
    val somethingNotNull: String = "aString"
    // somethingNotNull: String = null => compilation error

    var length = somethingNotNull.length

    var something: String? = null
    length = something?.length ?: 0
    length = createSomething()?.length ?: 0

    // length = createSomething()!!.length // throw kotlin.KotlinNullPointerException

    // SmartCast
    something = "aString"
    length = something.length // auto cast to String (no need of `?.`)
}

fun createSomething(): String? = null

null-safety.java

import kotlin.Metadata;
import org.jetbrains.annotations.Nullable;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u000e\n\u0000\n\u0002\u0010\u000e\n\u0000\n\u0002\u0010\u0002\n\u0000\u001a\b\u0010\u0000\u001a\u0004\u0018\u00010\u0001\u001a\u0006\u0010\u0002\u001a\u00020\u0003¨\u0006\u0004"},
        d2 = {"createSomething", "", "main", "", "kotlinDee"}
)
public final class Null_safetyKt {
   public static final void main() {
      String somethingNotNull = "aString";
      int length = somethingNotNull.length();
      String something = (String)null;
      int length = false;
      String var10000 = createSomething();
      length = var10000 != null ? var10000.length() : 0;
      something = "aString";
      length = something.length();
   }

   // $FF: synthetic method
   public static void main(String[] var0) {
      main();
   }

   @Nullable
   public static final String createSomething() {
      return null;
   }
}

Bilan null-safety

🎸 Elvis operator: ?:
🙌 plus de NullPointerException
⚠️ quand on appelle du Java
Le compilateur Kotlin peut interpréter des annotions de nullabilité (JSR-305, Android, ...)
Pas de Optional, si nécessaire voir Arrow

Les types

Types basiques

Types de base de Kotlin

Types basiques nullable

Types de base de Kotlin nullable

todo.kt

fun `is P = NP`(): Boolean =
    TODO()

fun main(args: Array<String>) {
    println("P = NP is ${`is P = NP`()}")
}

Hiérarchie des types

🤝 le TODO() est l'ami du TDD

Les fonctions

named-params.kt

fun buildString(prefix: String,
                who: String,
                enhanced: Boolean): String {
    var msg = "$prefix $who"
    if (enhanced) {
        msg += '!'
    }
    return msg
}

fun greetings(): String =
    buildString(enhanced = true, who = "RivieraDev", prefix = "Hello")

named-params.java

import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u0012\n\u0000\n\u0002\u0010\u000e\n\u0002\b\u0003\n\u0002\u0010\u000b\n\u0002\b\u0002\u001a\u001e\u0010\u0000\u001a\u00020\u00012\u0006\u0010\u0002\u001a\u00020\u00012\u0006\u0010\u0003\u001a\u00020\u00012\u0006\u0010\u0004\u001a\u00020\u0005\u001a\u0006\u0010\u0006\u001a\u00020\u0001¨\u0006\u0007"},
        d2 = {"buildString", "", "prefix", "who", "enhanced", "", "greetings", "kotlinDee"}
)
public final class Named_paramsKt {
   @NotNull
   public static final String buildString(@NotNull String prefix, @NotNull String who, boolean enhanced) {
      Intrinsics.checkParameterIsNotNull(prefix, "prefix");
      Intrinsics.checkParameterIsNotNull(who, "who");
      String msg = prefix + ' ' + who;
      if (enhanced) {
         msg = msg + '!';
      }

      return msg;
   }

   @NotNull
   public static final String greetings() {
      String var0 = "Hello";
      String var1 = "RivieraDev";
      boolean var2 = true;
      return buildString(var0, var1, var2);
   }
}

default-value.kt

fun buildString2(prefix: String = "Hello",
                 who: String,
                 enhanced: Boolean = true): String {
    var msg = "$prefix $who"
    if (enhanced) {
        msg += '!'
    }
    return msg
}

fun greetings2(): String =
    buildString2(who = "RivieraDev")

Comment ça marche

// In my-app.jar
fun main() {
    println(compute())
}

// In lib-v1.0.0
fun compute(result: Int = 1) = result

// In lib-v1.0.1
fun compute(result: Int = 42) = result

Compile my-app avec lib-v1.0.0
java my-app.jar -cp lib-v1.0.0.jar
java my-app.jar -cp lib-v1.0.1.jar
Résultat ?

default-value.java

import kotlin.Metadata;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\b\n\u0000\n\u0002\u0010\u0002\n\u0000\u001a\u0006\u0010\u0000\u001a\u00020\u0001¨\u0006\u0002"},
        d2 = {"main", "", "kotlinDee"}
)
public final class My_appKt {
    public static final void main() {
        int var0 = LibKt.compute$default(0, 1, (Object)null);
        boolean var1 = false;
        System.out.println(var0);
    }

    // $FF: synthetic method
    public static void main(String[] var0) {
        main();
    }
}

ByteCode de default-value

import kotlin.Metadata;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\n\n\u0000\n\u0002\u0010\b\n\u0002\b\u0002\u001a\u0010\u0010\u0000\u001a\u00020\u00012\b\b\u0002\u0010\u0002\u001a\u00020\u0001¨\u0006\u0003"},
        d2 = {"compute", "", "result", "kotlinDee"}
)
public final class LibKt {
    public static final int compute(int result) {
        return result;
    }

    // $FF: synthetic method
    public static int compute$default(int var0, int var1, Object var2) {
        if ((var1 & 1) != 0) {
            var0 = 42;
        }

        return compute(var0);
    }
}

Kotlin c'est fun !

Toujours typer le retour de vos fonctions
(sauf si c'est évident et une surcharge comme le toString)
Kotlin est plus concis que Java
=> évitez de faire des fonctions trop longues
Sautez une ligne après le =
Utilisez le passage des arguments par nom quand ça lève des ambiguïtés

Les lambdas

function.kt

// Declare apply function with function as parameter
fun compute(x: Int, y: Int, operation: (Int, Int) -> Int): Int =
    operation(x, y)

// Declare function
fun sumf(x: Int, y: Int): Int =
    x + y

// call compute with function reference
val sum5 = compute(2, 3, ::sumf)

// store function reference
val sumLam = ::sumf

// call compute with the function reference
val sum6 = compute(1, 5, sumLam)

function.java

import kotlin.Metadata;
import kotlin.jvm.functions.Function2;
import kotlin.jvm.internal.Intrinsics;
import kotlin.reflect.KFunction;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u001e\n\u0000\n\u0002\u0010\b\n\u0002\b\u0005\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0002\b\u0007\n\u0002\u0018\u0002\n\u0002\b\u0002\u001a0\u0010\u000e\u001a\u00020\u00012\u0006\u0010\n\u001a\u00020\u00012\u0006\u0010\u000b\u001a\u00020\u00012\u0018\u0010\u000f\u001a\u0014\u0012\u0004\u0012\u00020\u0001\u0012\u0004\u0012\u00020\u0001\u0012\u0004\u0012\u00020\u00010\u0010\u001a\u0016\u0010\u0011\u001a\u00020\u00012\u0006\u0010\n\u001a\u00020\u00012\u0006\u0010\u000b\u001a\u00020\u0001\"\u0011\u0010\u0000\u001a\u00020\u0001¢\u0006\b\n\u0000\u001a\u0004\b\u0002\u0010\u0003\"\u0011\u0010\u0004\u001a\u00020\u0001¢\u0006\b\n\u0000\u001a\u0004\b\u0005\u0010\u0003\"A\u0010\u0006\u001a2\u0012\u0013\u0012\u00110\u0001¢\u0006\f\b\b\u0012\b\b\t\u0012\u0004\b\b(\n\u0012\u0013\u0012\u00110\u0001¢\u0006\f\b\b\u0012\b\b\t\u0012\u0004\b\b(\u000b\u0012\u0004\u0012\u00020\u00010\u0007¢\u0006\b\n\u0000\u001a\u0004\b\f\u0010\r¨\u0006\u0012"},
        d2 = {"sum5", "", "getSum5", "()I", "sum6", "getSum6", "sumLam", "Lkotlin/reflect/KFunction2;", "Lkotlin/ParameterName;", "name", "x", "y", "getSumLam", "()Lkotlin/reflect/KFunction;", "compute", "operation", "Lkotlin/Function2;", "sumf", "kotlinDee"}
)
public final class FunctionKt {
   private static final int sum5;
   @NotNull
   private static final KFunction sumLam;
   private static final int sum6;

   public static final int compute(int x, int y, @NotNull Function2 operation) {
      Intrinsics.checkParameterIsNotNull(operation, "operation");
      return ((Number)operation.invoke(x, y)).intValue();
   }

   public static final int sumf(int x, int y) {
      return x + y;
   }

   public static final int getSum5() {
      return sum5;
   }

   @NotNull
   public static final KFunction getSumLam() {
      return sumLam;
   }

   public static final int getSum6() {
      return sum6;
   }

   static {
      sum5 = compute(2, 3, (Function2)null.INSTANCE);
      sumLam = null.INSTANCE;
      sum6 = compute(1, 5, (Function2)sumLam);
   }
}

lambda.kt

// Declare lambda
val suml: (Int, Int) -> Int = { x: Int, y: Int ->
    x + y
}

// call compute with suml lambda
val sum3 = compute(1, 2, suml)

// call compute with lamda
val sum4 = compute(1, 3) { x, y ->
    x + y
}

lambda.java

import kotlin.Metadata;
import kotlin.jvm.functions.Function2;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u0012\n\u0000\n\u0002\u0010\b\n\u0002\b\u0005\n\u0002\u0018\u0002\n\u0002\b\u0003\"\u0011\u0010\u0000\u001a\u00020\u0001¢\u0006\b\n\u0000\u001a\u0004\b\u0002\u0010\u0003\"\u0011\u0010\u0004\u001a\u00020\u0001¢\u0006\b\n\u0000\u001a\u0004\b\u0005\u0010\u0003\"#\u0010\u0006\u001a\u0014\u0012\u0004\u0012\u00020\u0001\u0012\u0004\u0012\u00020\u0001\u0012\u0004\u0012\u00020\u00010\u0007¢\u0006\b\n\u0000\u001a\u0004\b\b\u0010\t¨\u0006\n"},
        d2 = {"sum3", "", "getSum3", "()I", "sum4", "getSum4", "suml", "Lkotlin/Function2;", "getSuml", "()Lkotlin/jvm/functions/Function2;", "kotlinDee"}
)
public final class LambdaKt {
   @NotNull
   private static final Function2 suml;
   private static final int sum3;
   private static final int sum4;

   @NotNull
   public static final Function2 getSuml() {
      return suml;
   }

   public static final int getSum3() {
      return sum3;
   }

   public static final int getSum4() {
      return sum4;
   }

   static {
      suml = (Function2)null.INSTANCE;
      sum3 = FunctionKt.compute(1, 2, suml);
      sum4 = FunctionKt.compute(1, 3, (Function2)null.INSTANCE);
   }
}

let.kt

val other = sumf(1, 2)
    .let { it + 1 }

val nullable = maybeAnInt()
    ?.let { it + 1 }

let.java

import kotlin.Metadata;
import org.jetbrains.annotations.Nullable;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\n\n\u0000\n\u0002\u0010\b\n\u0002\b\u0007\"\u0015\u0010\u0000\u001a\u0004\u0018\u00010\u0001¢\u0006\n\n\u0002\u0010\u0004\u001a\u0004\b\u0002\u0010\u0003\"\u0011\u0010\u0005\u001a\u00020\u0001¢\u0006\b\n\u0000\u001a\u0004\b\u0006\u0010\u0007¨\u0006\b"},
        d2 = {"nullable", "", "getNullable", "()Ljava/lang/Integer;", "Ljava/lang/Integer;", "other", "getOther", "()I", "kotlinDee"}
)
public final class LetKt {
   private static final int other;
   @Nullable
   private static final Integer nullable;

   public static final int getOther() {
      return other;
   }

   @Nullable
   public static final Integer getNullable() {
      return nullable;
   }

   static {
      int var0 = FunctionKt.sumf(1, 2);
      boolean var1 = false;
      boolean var2 = false;
      int var4 = false;
      other = var0 + 1;
      Integer var10000 = PlopKt.maybeAnInt();
      if (var10000 != null) {
         Integer var5 = var10000;
         var1 = false;
         var2 = false;
         int it = ((Number)var5).intValue();
         var4 = false;
         var10000 = it + 1;
      } else {
         var10000 = null;
      }

      nullable = var10000;
   }
}

Les lambdas

⚠️ pas de return
pensez à mettre vos lambda comme dernier argument
voir aussi les apply, also, run , use, with
the tldr; on Kotlin’s let, apply, also, with and run functions

Les classes

astronomy.kt

interface AstronomicalBody {
    val name: String
}

data class Planet(override val name: String,
                  val moons: List<Moon> = emptyList()) : AstronomicalBody {
    init {
        require(name.isNotEmpty())
    }

    operator fun plus(moon: Moon): Planet {
        return this.copy(moons = moons + moon)
    }
}

data class Moon(override val name: String) : AstronomicalBody

object SolarSystem {
    val moon = Moon(name = "Moon")
    val earth = Planet(name = "Earth") + moon

    val bodies: List<AstronomicalBody> = listOf(
        earth,
        Planet(name = "Jupiter")
    )
}

enum class PlanetKind {
    Terrestrial, GasGiant, IceGiant;

    companion object {
        fun fromName(name: String): PlanetKind {
            return PlanetKind.valueOf(name) // enumValueOf(name)
        }
    }
}

fun getMoons(planet: Planet): List<Moon> {
    val (_, moons) = planet
    return moons
}

astronomy.java

import java.util.Collection;
import java.util.List;
import kotlin.Metadata;
import kotlin.collections.CollectionsKt;
import kotlin.jvm.internal.DefaultConstructorMarker;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 1,
        d1 = {"\u00000\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0000\n\u0002\u0010\u000e\n\u0000\n\u0002\u0010 \n\u0002\u0018\u0002\n\u0002\b\t\n\u0002\u0010\u000b\n\u0000\n\u0002\u0010\u0000\n\u0000\n\u0002\u0010\b\n\u0002\b\u0004\b\u0086\b\u0018\u00002\u00020\u0001B\u001d\u0012\u0006\u0010\u0002\u001a\u00020\u0003\u0012\u000e\b\u0002\u0010\u0004\u001a\b\u0012\u0004\u0012\u00020\u00060\u0005¢\u0006\u0002\u0010\u0007J\t\u0010\f\u001a\u00020\u0003HÆ\u0003J\u000f\u0010\r\u001a\b\u0012\u0004\u0012\u00020\u00060\u0005HÆ\u0003J#\u0010\u000e\u001a\u00020\u00002\b\b\u0002\u0010\u0002\u001a\u00020\u00032\u000e\b\u0002\u0010\u0004\u001a\b\u0012\u0004\u0012\u00020\u00060\u0005HÆ\u0001J\u0013\u0010\u000f\u001a\u00020\u00102\b\u0010\u0011\u001a\u0004\u0018\u00010\u0012HÖ\u0003J\t\u0010\u0013\u001a\u00020\u0014HÖ\u0001J\u0011\u0010\u0015\u001a\u00020\u00002\u0006\u0010\u0016\u001a\u00020\u0006H\u0086\u0002J\t\u0010\u0017\u001a\u00020\u0003HÖ\u0001R\u0017\u0010\u0004\u001a\b\u0012\u0004\u0012\u00020\u00060\u0005¢\u0006\b\n\u0000\u001a\u0004\b\b\u0010\tR\u0014\u0010\u0002\u001a\u00020\u0003X\u0096\u0004¢\u0006\b\n\u0000\u001a\u0004\b\n\u0010\u000b¨\u0006\u0018"},
        d2 = {"LPlanet;", "LAstronomicalBody;", "name", "", "moons", "", "LMoon;", "(Ljava/lang/String;Ljava/util/List;)V", "getMoons", "()Ljava/util/List;", "getName", "()Ljava/lang/String;", "component1", "component2", "copy", "equals", "", "other", "", "hashCode", "", "plus", "moon", "toString", "kotlinDee"}
)
public final class Planet implements AstronomicalBody {
   @NotNull
   private final String name;
   @NotNull
   private final List moons;

   @NotNull
   public final Planet plus(@NotNull Moon moon) {
      Intrinsics.checkParameterIsNotNull(moon, "moon");
      return copy$default(this, (String)null, CollectionsKt.plus((Collection)this.moons, moon), 1, (Object)null);
   }

   @NotNull
   public String getName() {
      return this.name;
   }

   @NotNull
   public final List getMoons() {
      return this.moons;
   }

   public Planet(@NotNull String name, @NotNull List moons) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      Intrinsics.checkParameterIsNotNull(moons, "moons");
      super();
      this.name = name;
      this.moons = moons;
      CharSequence var3 = (CharSequence)this.getName();
      boolean var4 = false;
      boolean var8 = var3.length() > 0;
      var4 = false;
      boolean var5 = false;
      var5 = false;
      boolean var6 = false;
      if (!var8) {
         boolean var7 = false;
         String var9 = "Failed requirement.";
         throw (Throwable)(new IllegalArgumentException(var9.toString()));
      }
   }

   // $FF: synthetic method
   public Planet(String var1, List var2, int var3, DefaultConstructorMarker var4) {
      if ((var3 & 2) != 0) {
         var2 = CollectionsKt.emptyList();
      }

      this(var1, var2);
   }

   @NotNull
   public final String component1() {
      return this.getName();
   }

   @NotNull
   public final List component2() {
      return this.moons;
   }

   @NotNull
   public final Planet copy(@NotNull String name, @NotNull List moons) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      Intrinsics.checkParameterIsNotNull(moons, "moons");
      return new Planet(name, moons);
   }

   // $FF: synthetic method
   @NotNull
   public static Planet copy$default(Planet var0, String var1, List var2, int var3, Object var4) {
      if ((var3 & 1) != 0) {
         var1 = var0.getName();
      }

      if ((var3 & 2) != 0) {
         var2 = var0.moons;
      }

      return var0.copy(var1, var2);
   }

   @NotNull
   public String toString() {
      return "Planet(name=" + this.getName() + ", moons=" + this.moons + ")";
   }

   public int hashCode() {
      String var10000 = this.getName();
      int var1 = (var10000 != null ? var10000.hashCode() : 0) * 31;
      List var10001 = this.moons;
      return var1 + (var10001 != null ? var10001.hashCode() : 0);
   }

   public boolean equals(@Nullable Object var1) {
      if (this != var1) {
         if (var1 instanceof Planet) {
            Planet var2 = (Planet)var1;
            if (Intrinsics.areEqual(this.getName(), var2.getName()) && Intrinsics.areEqual(this.moons, var2.moons)) {
               return true;
            }
         }

         return false;
      } else {
         return true;
      }
   }
}

Héritage en Kotlin

open class SmallBody {
    open fun sizeRange(): IntRange = 0..10
}

// Inherit SmallBody
data class Comet(val name: String): SmallBody()

// Inherit SmallBody
data class Asteroid(val name: String): SmallBody() {
    override fun sizeRange(): IntRange = 0..4
}

fun main(args: Array<String>) {
    val bodies = listOf(Comet("Halley"), Asteroid("Adeona"))

    bodies.forEach { body ->
        println("$body: ${body.sizeRange()}")
    }
}

Génériques

⚠️ Les contrôles de types génériques ne sont faits qu'au moment de la compilation
Covariant: out, en java ? extends T
Contravariant: in, en java ? super T
Projection * correspondant à Any? ou Nothing

Borne supérieure

fun <T : Comparable<T>> sort(list: List<T>): List<T>

Les détails: https://kotlinlang.org/docs/reference/generics.html

Sealed

sealed class JsonValue

data class JsonObject(val attributes: Map<String, JsonValue>) : JsonValue()
data class JsonArray(val values: List<JsonValue>) : JsonValue()
data class JsonString(val value: String) : JsonValue()
data class JsonNumber(val value: Number) : JsonValue()
data class JsonBoolean(val value: Boolean) : JsonValue()
object JsonNull : JsonValue()

Alias en Kotlin

interface Entity

typealias Id = String
typealias Version = Int
typealias EntityKey = Pair<Id, Version>
typealias Entities = List<Entity>

// fun getAllEntities(): Map<Pair<String, Int>, List<Entity>> = emptyMap()
fun getAllEntities(): Map<EntityKey, Entities> = emptyMap()

ByteCode d'alias

Compiled from "typealias.kt"
public final class TypealiasKt {
  public static final java.util.Map<kotlin.Pair<java.lang.String, java.lang.Integer>, java.util.List<Entity>> getAllEntities();
    Code:
       0: invokestatic  #13                 // Method kotlin/collections/MapsKt.emptyMap:()Ljava/util/Map;
       3: areturn
}

Classe, le bilan

🤩 data class
🤔 Mais pourquoi on n'a pas ça en Java ?
JEP draft: Records and Sealed Types
Une seule classe par fichier n'est pas utile
🤓 sealed permet de faire des types algébriques de données (Algebraic Data Type)

Pause

ByteCode Android

Compilation pour Android

Compile Android

Dalvik EXecutable format

Dalvik Executable format

java -jar ./scripts/lib/d8.jar --release \
            --output ./target/android/dex \
            ./target/android/hello.jar

00000000  64 65 78 0a 30 33 35 00  06 50 f0 61 50 10 7c c0  |dex.035..P.aP.|.|
00000010  b2 f9 77 2d 54 df 60 f3  ac dd b0 10 eb 55 53 e1  |..w-T.`......US.|
00000020  28 f6 10 00 70 00 00 00  78 56 34 12 00 00 00 00  |(...p...xV4.....|
00000030  00 00 00 00 4c f5 10 00  12 17 00 00 70 00 00 00  |....L.......p...|
00000040  31 03 00 00 b8 5c 00 00  2a 08 00 00 7c 69 00 00  |1....\..*...|i..|
00000050  30 03 00 00 74 cb 00 00  20 1a 00 00 f4 e4 00 00  |0...t... .......|
00000060  75 02 00 00 f4 b5 01 00  94 f1 0e 00 94 04 02 00  |u...............|
00000070  4a f1 07 00 4c f1 07 00  75 f1 07 00 a4 f1 07 00  |J...L...u.......|
00000080  c2 f1 07 00 e0 f1 07 00  00 f2 07 00 23 f2 07 00  |............#...|
00000090  71 f2 07 00 b9 f2 07 00  07 f3 07 00 37 f3 07 00  |q...........7...|
000000a0  69 f3 07 00 90 f3 07 00  bc f3 07 00 e3 f3 07 00  |i...............|
000000b0  27 f4 07 00 71 f4 07 00  8f f4 07 00 ad f4 07 00  |'...q...........|
000000c0  cb f4 07 00 ed f4 07 00  0f f5 07 00 2c f5 07 00  |............,...|
000000d0  49 f5 07 00 79 f5 07 00  b1 f5 07 00 e9 f5 07 00  |I...y...........|
000000e0  1a f6 07 00 51 f6 07 00  7b f6 07 00 a6 f6 07 00  |....Q...{.......|
000000f0  d1 f6 07 00 0a f7 07 00  47 f7 07 00 84 f7 07 00  |........G.......|
00000100  c1 f7 07 00 02 f8 07 00  43 f8 07 00 84 f8 07 00  |........C.......|
00000110  f1 f8 07 00 12 f9 07 00  41 f9 07 00 6e f9 07 00  |........A...n...|
00000120  b0 f9 07 00 dd f9 07 00  0a fa 07 00 39 fa 07 00  |............9...|
00000130  68 fa 07 00 ab fa 07 00  e0 fa 07 00 25 fb 07 00  |h...........%...|
00000140  f3 fb 07 00 3b fc 07 00  79 fc 07 00 b1 fc 07 00  |....;...y.......|
00000150  eb fc 07 00 26 fd 07 00  68 fd 07 00 9e fd 07 00  |....&...h.......|
00000160  e7 fd 07 00 2a fe 07 00  5c fe 07 00 9d fe 07 00  |....*...\.......|
00000170  de fe 07 00 25 ff 07 00  5b ff 07 00 90 ff 07 00  |....%...[.......|
00000180  c0 ff 07 00 fc ff 07 00  75 00 08 00 ca 00 08 00  |........u.......|
00000190  30 01 08 00 a7 01 08 00  2f 02 08 00 c9 02 08 00  |0......./.......|
000001a0  74 03 08 00 30 04 08 00  fd 04 08 00 db 05 08 00  |t...0...........|
000001b0  ca 06 08 00 ca 07 08 00  db 08 08 00 fd 09 08 00  |................|
000001c0  30 0b 08 00 76 0c 08 00  cd 0d 08 00 35 0f 08 00  |0...v.......5...|
000001d0  ae 10 08 00 38 12 08 00  d3 13 08 00 7f 15 08 00  |....8...........|
000001e0  3c 17 08 00 7b 17 08 00  b8 17 08 00 f5 17 08 00  |<...{...........|
000001f0  34 18 08 00 80 18 08 00  cc 18 08 00 18 19 08 00  |4...............|
00000200  64 19 08 00 b0 19 08 00  fc 19 08 00 48 1a 08 00  |d...........H...|
00000210  94 1a 08 00 c8 1a 08 00  ff 1a 08 00 3f 1b 08 00  |............?...|
00000220  87 1b 08 00 62 1c 08 00  a8 1c 08 00 16 1d 08 00  |....b...........|
00000230  57 1d 08 00 a4 1d 08 00  e8 1d 08 00 31 1e 08 00  |W...........1...|
00000240  86 1e 08 00 d1 1e 08 00  23 1f 08 00 7a 1f 08 00  |........#...z...|
00000250  bf 1f 08 00 06 20 08 00  4d 20 08 00 f8 20 08 00  |..... ..M ... ..|
00000260  4f 21 08 00 84 21 08 00  b9 21 08 00 f8 21 08 00  |O!...!...!...!..|
00000270  4e 22 08 00 9d 22 08 00  e7 22 08 00 21 23 08 00  |N"..."..."..!#..|
00000280  6b 23 08 00 d2 23 08 00  0e 24 08 00 4a 24 08 00  |k#...#...$..J$..|
00000290  8d 24 08 00 e1 24 08 00  43 25 08 00 c6 25 08 00  |.$...$..C%...%..|
000002a0  14 26 08 00 6c 26 08 00  b9 26 08 00 0c 27 08 00  |.&..l&...&...'..|
000002b0  61 27 08 00 9f 27 08 00  e3 27 08 00 55 28 08 00  |a'...'...'..U(..|
000002c0  d1 28 08 00 2a 29 08 00  db 29 08 00 8c 2a 08 00  |.(..*)...)...*..|
000002d0  e5 2a 08 00 3e 2b 08 00  97 2b 08 00 e6 2b 08 00  |.*..>+...+...+..|
000002e0  8c 2c 08 00 a5 2f 08 00  ed 2f 08 00 1a 31 08 00  |.,.../.../...1..|
000002f0  6f 31 08 00 c4 31 08 00  31 32 08 00 88 32 08 00  |o1...1..12...2..|
00000300  fa 32 08 00 87 33 08 00  2c 34 08 00 75 34 08 00  |.2...3..,4..u4..|
00000310  da 34 08 00 85 35 08 00  ed 35 08 00 50 36 08 00  |.4...5...5..P6..|
00000320  a1 36 08 00 fe 36 08 00  48 37 08 00 8e 37 08 00  |.6...6..H7...7..|
00000330  ce 37 08 00 6f 38 08 00  dc 38 08 00 23 39 08 00  |.7..o8...8..#9..|
00000340  64 39 08 00 a1 39 08 00  f4 39 08 00 47 3a 08 00  |d9...9...9..G:..|
00000350  b1 3a 08 00 0f 3b 08 00  ae 3b 08 00 5a 3c 08 00  |.:...;...;..Z<..|
00000360  e4 3c 08 00 c0 3d 08 00  4a 3e 08 00 ae 3e 08 00  |.<...=..J>...>..|
00000370  0f 3f 08 00 b0 3f 08 00  83 40 08 00 f4 40 08 00  |.?...?...@...@..|
00000380  3f 41 08 00 8b 41 08 00  06 42 08 00 6d 42 08 00  |?A...A...B..mB..|
00000390  14 43 08 00 a7 43 08 00  0e 44 08 00 75 44 08 00  |.C...C...D..uD..|
000003a0  41 45 08 00 9b 45 08 00  f5 45 08 00 61 46 08 00  |AE...E...E..aF..|
000003b0  14 47 08 00 c7 47 08 00  25 48 08 00 78 48 08 00  |.G...G..%H..xH..|
000003c0  11 49 08 00 d7 49 08 00  44 4a 08 00 b3 4a 08 00  |.I...I..DJ...J..|
000003d0  20 4b 08 00 b1 4b 08 00  d7 4d 08 00 58 4e 08 00  | K...K...M..XN..|
000003e0  f5 4e 08 00 99 4f 08 00  36 50 08 00 cd 50 08 00  |.N...O..6P...P..|
000003f0  44 51 08 00 c4 51 08 00  3d 52 08 00 af 52 08 00  |DQ...Q..=R...R..|
00000400  2c 53 08 00 aa 53 08 00  15 54 08 00 af 54 08 00  |,S...S...T...T..|
00000410  4a 55 08 00 68 56 08 00  7b 57 08 00 5a 58 08 00  |JU..hV..{W..ZX..|
00000420  19 59 08 00 1c 5a 08 00  13 5b 08 00 91 5b 08 00  |.Y...Z...[...[..|
00000430  f8 5b 08 00 7c 5c 08 00  5d 5d 08 00 2a 5e 08 00  |.[..|\..]]..*^..|
00000440  8d 5e 08 00 41 5f 08 00  ef 5f 08 00 ab 60 08 00  |.^..A_..._...`..|
00000450  2f 61 08 00 ba 61 08 00  54 62 08 00 4a 63 08 00  |/a...a..Tb..Jc..|
00000460  2c 64 08 00 8d 64 08 00  58 65 08 00 dc 65 08 00  |,d...d..Xe...e..|
00000470  5c 66 08 00 dc 66 08 00  43 67 08 00 eb 67 08 00  |\f...f..Cg...g..|
00000480  71 68 08 00 f5 68 08 00  9a 69 08 00 5a 6a 08 00  |qh...h...i..Zj..|
00000490  1a 6b 08 00 e5 6c 08 00  3d 76 08 00 42 77 08 00  |.k...l..=v..Bw..|
000004a0  c5 77 08 00 8e 78 08 00  39 79 08 00 15 7a 08 00  |.w...x..9y...z..|
000004b0  f4 7a 08 00 06 7c 08 00  95 7c 08 00 63 7d 08 00  |.z...|...|..c}..|
000004c0  03 7e 08 00 b9 7e 08 00  73 7f 08 00 4b 80 08 00  |.~...~..s...K...|
000004d0  cf 80 08 00 8a 81 08 00  13 82 08 00 a0 82 08 00  |................|
000004e0  6f 83 08 00 1b 84 08 00  ce 84 08 00 9d 85 08 00  |o...............|
000004f0  2a 86 08 00 ee 86 08 00  7f 88 08 00 84 89 08 00  |*...............|
00000500  54 8a 08 00 22 8b 08 00  34 8c 08 00 47 8d 08 00  |T..."...4...G...|
00000510  f7 8d 08 00 7d 8e 08 00  03 8f 08 00 89 8f 08 00  |....}...........|
00000520  0f 90 08 00 95 90 08 00  1b 91 08 00 a0 91 08 00  |................|
00000530  25 92 08 00 aa 92 08 00  2f 93 08 00 b4 93 08 00  |%......./.......|
00000540  39 94 08 00 be 94 08 00  4d 95 08 00 52 96 08 00  |9.......M...R...|
00000550  02 97 08 00 16 98 08 00  b1 99 08 00 35 9a 08 00  |............5...|
00000560  ca 9a 08 00 56 9b 08 00  c2 9c 08 00 dc 9d 08 00  |....V...........|
00000570  8b 9e 08 00 95 9f 08 00  4e a1 08 00 7d a2 08 00  |........N...}...|
00000580  66 a3 08 00 61 a4 08 00  fe a4 08 00 93 a5 08 00  |f...a...........|
00000590  2e a6 08 00 f3 a6 08 00  bb a7 08 00 83 a8 08 00  |................|
000005a0  4b a9 08 00 13 aa 08 00  db aa 08 00 a3 ab 08 00  |K...............|
000005b0  8a ac 08 00 6a ad 08 00  3e ae 08 00 f6 ae 08 00  |....j...>.......|
000005c0  b0 b0 08 00 ab b1 08 00  94 b2 08 00 bb b3 08 00  |................|
000005d0  2a b5 08 00 bf b5 08 00  40 b6 08 00 2f b7 08 00  |*.......@.../...|
000005e0  47 b8 08 00 5f b9 08 00  3c ba 08 00 b7 bb 08 00  |G..._...<.......|
000005f0  a9 bc 08 00 d3 bd 08 00  eb be 08 00 f0 bf 08 00  |................|
00000600  b9 c0 08 00 59 c1 08 00  4b c2 08 00 08 c3 08 00  |....Y...K.......|
00000610  d5 c3 08 00 d6 c4 08 00  36 c6 08 00 86 c7 08 00  |........6.......|
00000620  66 c8 08 00 65 c9 08 00  e3 ca 08 00 d9 cb 08 00  |f...e...........|
00000630  b0 cc 08 00 d0 cd 08 00  6b cf 08 00 4f d0 08 00  |........k...O...|
00000640  33 d1 08 00 0e d2 08 00  2c d5 08 00 72 da 08 00  |3.......,...r...|
00000650  69 db 08 00 88 dd 08 00  99 df 08 00 83 e0 08 00  |i...............|
00000660  3c e3 08 00 c7 e4 08 00  5f e6 08 00 2b e7 08 00  |<......._...+...|
00000670  e6 e8 08 00 9a ea 08 00  40 eb 08 00 e3 ed 08 00  |........@.......|
00000680  59 f5 08 00 85 f6 08 00  bd f7 08 00 ac f8 08 00  |Y...............|
00000690  86 fa 08 00 f4 fb 08 00  83 fd 08 00 9e ff 08 00  |................|
000006a0  0d 01 09 00 e8 01 09 00  9e 03 09 00 50 06 09 00  |............P...|
000006b0  ff 08 09 00 a3 0b 09 00  40 12 09 00 66 14 09 00  |........@...f...|
000006c0  89 15 09 00 1e 17 09 00  76 19 09 00 1f 1b 09 00  |........v.......|
000006d0  ab 1c 09 00 99 1e 09 00  32 20 09 00 77 22 09 00  |........2 ..w"..|
000006e0  e7 25 09 00 a2 27 09 00  46 2a 09 00 8f 36 09 00  |.%...'..F*...6..|
000006f0  d2 38 09 00 65 40 09 00  20 43 09 00 35 46 09 00  |.8..e@.. C..5F..|
00000700  5f 4d 09 00 5f 5b 09 00  46 61 09 00 00 68 09 00  |_M.._[..Fa...h..|
00000710  06 6b 09 00 d6 7e 09 00  e5 9f 09 00 e7 9f 0a 00  |.k...~..........|
00000720  72 b7 0a 00 b5 e4 0a 00  7b eb 0a 00 7e eb 0a 00  |r.......{...~...|
00000730  81 eb 0a 00 85 eb 0a 00  8b eb 0a 00 b2 eb 0a 00  |................|
00000740  b8 eb 0a 00 bd eb 0a 00  cb eb 0a 00 d2 eb 0a 00  |................|
00000750  de eb 0a 00 f9 eb 0a 00  0e ec 0a 00 18 ec 0a 00  |................|
00000760  33 ec 0a 00 4b ec 0a 00  60 ec 0a 00 79 ec 0a 00  |3...K...`...y...|
00000770  8b ec 0a 00 d2 ec 0a 00  1d ed 0a 00 2c ed 0a 00  |............,...|
00000780  49 ed 0a 00 5e ed 0a 00  71 ed 0a 00 95 ed 0a 00  |I...^...q.......|
00000790  9d ed 0a 00 b7 ed 0a 00  c3 ed 0a 00 da ed 0a 00  |................|
000007a0  f0 ed 0a 00 f9 ed 0a 00  02 ee 0a 00 0a ee 0a 00  |................|
000007b0  22 ee 0a 00 2f ee 0a 00  3c ee 0a 00 49 ee 0a 00  |".../...<...I...|
000007c0  5e ee 0a 00 6b ee 0a 00  7c ee 0a 00 86 ee 0a 00  |^...k...|.......|
000007d0  91 ee 0a 00 a1 ee 0a 00  ae ee 0a 00 b7 ee 0a 00  |................|
000007e0  bf ee 0a 00 ce ee 0a 00  d6 ee 0a 00 e1 ee 0a 00  |................|
000007f0  e7 ee 0a 00 f5 ee 0a 00  fd ee 0a 00 0c ef 0a 00  |................|
00000800  17 ef 0a 00 21 ef 0a 00  29 ef 0a 00 3a ef 0a 00  |....!...)...:...|
00000810  53 ef 0a 00 5f ef 0a 00  6a ef 0a 00 7d ef 0a 00  |S..._...j...}...|
00000820  87 ef 0a 00 90 ef 0a 00  9e ef 0a 00 b4 ef 0a 00  |................|
00000830  bb ef 0a 00 c6 ef 0a 00  d2 ef 0a 00 d9 ef 0a 00  |................|
00000840  e8 ef 0a 00 f5 ef 0a 00  fc ef 0a 00 0b f0 0a 00  |................|
00000850  17 f0 0a 00 27 f0 0a 00  2a f0 0a 00 2e f0 0a 00  |....'...*.......|
00000860  32 f0 0a 00 37 f0 0a 00  3c f0 0a 00 41 f0 0a 00  |2...7...<...A...|
00000870  46 f0 0a 00 4b f0 0a 00  67 f0 0a 00 79 f0 0a 00  |F...K...g...y...|
00000880  90 f0 0a 00 a4 f0 0a 00  bd f0 0a 00 d2 f0 0a 00  |................|
00000890  ec f0 0a 00 02 f1 0a 00  17 f1 0a 00 2e f1 0a 00  |................|
000008a0  42 f1 0a 00 58 f1 0a 00  6d f1 0a 00 83 f1 0a 00  |B...X...m.......|
000008b0  9c f1 0a 00 ba f1 0a 00  d4 f1 0a 00 ee f1 0a 00  |................|

dexdump

~/.android-sdk/build-tools/23.0.1/dexdump -d \
      ./target/android/dex/classes.dex \
      > ./target/android/dex/classes.dex.dump

Processing './target/android/dex/classes.dex'...
Opened './target/android/dex/classes.dex', DEX version '035'
Class #0            -
  Class descriptor  : 'L_00_helloworld/HelloWorldKt;'
  Access flags      : 0x0011 (PUBLIC FINAL)
  Superclass        : 'Ljava/lang/Object;'
  Interfaces        -
  Static fields     -
  Instance fields   -
  Direct methods    -
    #0              : (in L_00_helloworld/HelloWorldKt;)
      name          : 'main'
      type          : '([Ljava/lang/String;)V'
      access        : 0x0019 (PUBLIC STATIC FINAL)
      code          -
      registers     : 2
      ins           : 1
      outs          : 2
      insns size    : 13 16-bit code units
020494:                                        |[020494] _00_helloworld.HelloWorldKt.main:([Ljava/lang/String;)V
0204a4: 1a00 1310                              |0000: const-string v0, "args" // string@1013
0204a8: 7120 a811 0100                         |0002: invoke-static {v1, v0}, Lkotlin/jvm/internal/Intrinsics;.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V // method@11a8
0204ae: 1a01 0808                              |0005: const-string v1, "Hello RivieraDev" // string@0808
0204b2: 6200 0c00                              |0007: sget-object v0, Ljava/lang/System;.out:Ljava/io/PrintStream; // field@000c
0204b6: 6e20 3f00 1000                         |0009: invoke-virtual {v0, v1}, Ljava/io/PrintStream;.println:(Ljava/lang/Object;)V // method@003f
0204bc: 0e00                                   |000c: return-void
      catches       : (none)
      positions     :
        0x0007 line=4
      locals        :

  Virtual methods   -
  source_file_idx   : 2057 (HelloWorld.kt)
...

smali

sh ./scripts/lib/dextools/d2j-dex2smali.sh \
     ./target/android/dex/classes.dex -f \
     -o ./target/android/smali

.class public final L_00_helloworld/HelloWorldKt;
.super Ljava/lang/Object;
.source "HelloWorld.kt"

.annotation system Ldalvik/annotation/SourceDebugExtension;
  value = "SMAP\nHelloWorld.kt\nKotlin\n*S Kotlin\n*F\n+ 1 HelloWorld.kt\n_00_helloworld/HelloWorldKt\n*L\n1#1,5:1\n*E\n"
.end annotation
.annotation runtime Lkotlin/Metadata;
  bv = {
    1,
    0,
    2
  }
  d1 = {
    "\u0000\u0012\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0000\u001a\u0019\u0010\u0000\u001a\u00020\u00012\u000c\u0010\u0002\u001a\u0008\u0012\u0004\u0012\u00020\u00040\u0003\u00a2\u0006\u0002\u0010\u0005"
  }
  d2 = {
    "main",
    "",
    "args",
    "",
    "",
    "([Ljava/lang/String;)V"
  }
  k = 2
  mv = {
    1,
    1,
    9
  }
.end annotation

.method public final static main([Ljava/lang/String;)V
  .parameter # [Ljava/lang/String;
    .annotation build Lorg/jetbrains/annotations/NotNull;
    .end annotation
  .end parameter
  .registers 2
    const-string v0, "args"
    invoke-static { p0, v0 }, Lkotlin/jvm/internal/Intrinsics;->checkParameterIsNotNull(Ljava/lang/Object;Ljava/lang/String;)V
    const-string p0, "Hello RivieraDev"
  .line 4
    sget-object v0, Ljava/lang/System;->out:Ljava/io/PrintStream;
    invoke-virtual { v0, p0 }, Ljava/io/PrintStream;->println(Ljava/lang/Object;)V
    return-void
.end method

Autres structures

if-then-else.kt

fun handleAstronomicalBody(body: AstronomicalBody) {
    val message =
        if (body is Planet && body.name == "Earth") {
            "Welcome Earth"
        } else {
            "Welcome martian"
        }
    println(message)
}

for.kt

fun main(args: Array<String>) {
    for (body in SolarSystem.bodies) { // 🤢
        print(body)
    }
}

Mais aussi des while et do while

et des break, continue, et label

when.kt

for (body in SolarSystem.bodies) { // 🤢

    val message = when (body) {
        is Planet -> "Planet ${body.name}"
        is Star   -> "Star ${body.name}"
        else      -> null
    }

    if (message != null) {
        println(message)
    }
}

for-factorial.kt

// Note: assert(n >= 0)
fun forFactorial(n: Int): Int { // 🤢
    var acc = 1
    for (i in 1..n) {
        acc *= i
    }
    return acc
}

ByteCode factoriel avec for

Compiled from "for-factorial.kt"
public final class For_factorialKt {
  public static final int forFactorial(int);
    Code:
       0: iconst_1
       1: istore_1
       2: iconst_1
       3: istore_2
       4: iload_0
       5: istore_3
       6: iload_2
       7: iload_3
       8: if_icmpgt     26
      11: iload_1
      12: iload_2
      13: imul
      14: istore_1
      15: iload_2
      16: iload_3
      17: if_icmpeq     26
      20: iinc          2, 1
      23: goto          11
      26: iload_1
      27: ireturn
}

rec-factorial.kt

// Note: assert(n >= 0)
fun recFactorial(n: Int): Int =
    if (n < 1) 1
    else n * recFactorial(n - 1)

ByteCode factoriel avec récursivité

Compiled from "rec-factorial.kt"
public final class Rec_factorialKt {
  public static final int recFactorial(int);
    Code:
       0: iload_0
       1: iconst_1
       2: if_icmpge     9
       5: iconst_1
       6: goto          17
       9: iload_0
      10: iload_0
      11: iconst_1
      12: isub
      13: invokestatic  #8                  // Method recFactorial:(I)I
      16: imul
      17: ireturn
}

Récursion non terminale

`x! = x xx (x-1) xx ... xx 2 xx 1` `1! = 0! = 1`

`fact(x)`
`x xx fact(x-1)`
- `x`
`x xx (x-1) xx fact(x-2)`
- `x - 1`
- `x`
`x xx (x-1) xx (x-2) xx ...`
- ...
- `x - 1`
- `x`
`x xx (x-1) xx (x-2) xx ... xx 2 xx 1`
- `1`
- `2`
- ...
- `x - 1`
- `x`

Récursion terminale

`fact(x) = fact(x, 1)`
`fact(x-1, x xx 1)`
`fact(x-2, x xx (x-1))`
`fact(... , x xx (x-1) xx (x-2) xx ...)`
`fact(1, x xx (x-1) xx (x-2) xx ... xx 2)`
⚠️ Nécessite une optimisation par le compilateur

tailrec-factorial.kt

// Note: assert(n >= 0)
fun tailRecFactorial(n: Int): Int {

    tailrec fun aux(n: Int, acc: Int): Int =
        if (n < 1) acc
        else aux(n - 1, acc * n)

    return aux(n, 1)
}

ByteCode factoriel avec recursivité terminale 1/2

public final class Tailrec_factorialKt {
  public static final int tailRecFactorial(int);
    Code:
       0: getstatic     #12                 // Field Tailrec_factorialKt$tailRecFactorial$1.INSTANCE:LTailrec_factorialKt$tailRecFactorial$1;
       3: astore_1
       4: aload_1
       5: iload_0
       6: iconst_1
       7: invokevirtual #16                 // Method Tailrec_factorialKt$tailRecFactorial$1.invoke:(II)I
      10: ireturn
}

ByteCode factoriel avec recursivité terminale 2/2

Compiled from "tailrec-factorial.kt"
final class Tailrec_factorialKt$tailRecFactorial$1 extends kotlin.jvm.internal.Lambda implements kotlin.jvm.functions.Function2<java.lang.Integer, java.lang.Integer, java.lang.Integer> {
  public static final Tailrec_factorialKt$tailRecFactorial$1 INSTANCE;

  public java.lang.Object invoke(java.lang.Object, java.lang.Object);
    Code:
       0: aload_0
       1: aload_1
       2: checkcast     #11                 // class java/lang/Number
       5: invokevirtual #15                 // Method java/lang/Number.intValue:()I
       8: aload_2
       9: checkcast     #11                 // class java/lang/Number
      12: invokevirtual #15                 // Method java/lang/Number.intValue:()I
      15: invokevirtual #18                 // Method invoke:(II)I
      18: invokestatic  #24                 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      21: areturn

  public final int invoke(int, int);
    Code:
       0: iload_1
       1: iconst_1
       2: if_icmpge     9
       5: iload_2
       6: goto          25
       9: aload_0
      10: checkcast     #2                  // class Tailrec_factorialKt$tailRecFactorial$1
      13: pop
      14: iload_1
      15: iconst_1
      16: isub
      17: iload_2
      18: iload_1
      19: imul
      20: istore_2
      21: istore_1
      22: goto          0
      25: ireturn

  Tailrec_factorialKt$tailRecFactorial$1();
    Code:
       0: aload_0
       1: iconst_2
       2: invokespecial #34                 // Method kotlin/jvm/internal/Lambda."<init>":(I)V
       5: return

  static {};
    Code:
       0: new           #2                  // class Tailrec_factorialKt$tailRecFactorial$1
       3: dup
       4: invokespecial #56                 // Method "<init>":()V
       7: putstatic     #58                 // Field INSTANCE:LTailrec_factorialKt$tailRecFactorial$1;
      10: return
}

Performances sur 10!

JavaFor 433372259 ops/s

433372259 ops/s

KotlinFor 374900724 ops/s

374900724 ops/s

JavaRec 71945600 ops/s

71945600 ops/s

KotlinRec 75889169 ops/s

75889169 ops/s

JavaTailRec 74708349 ops/s

74708349 ops/s

KotlinTailRec 432005904 ops/s

432005904 ops/s

JavaReduce 21560856 ops/s

21560856 ops/s

KotlinReduce 99169023 ops/s

99169023 ops/s

Benchmark Factoriel

Bilan structures

when peut être utilisé avec
- des constantes
- plusieurs valeurs séparées par ,
- une expression
- avec is et un type (avec un 'smart cast')
privilégier les when si vous avez plus de 2 cas

si vous faites des fonctions récursives, faites les tailrec

Extensions de fonctions

extension.kt

val AstronomicalBody.size: Int
    get() = name.length

fun AstronomicalBody.display() = "Body $name $size"

fun main(args: Array<String>) {
    SolarSystem.bodies
        .forEach { println(it.display()) }
}

extension.java

import java.util.Iterator;
import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000 \n\u0000\n\u0002\u0010\b\n\u0002\u0018\u0002\n\u0002\b\u0003\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0003\u001a\u0019\u0010\u0005\u001a\u00020\u00062\f\u0010\u0007\u001a\b\u0012\u0004\u0012\u00020\t0\b¢\u0006\u0002\u0010\n\u001a\n\u0010\u000b\u001a\u00020\t*\u00020\u0002\"\u0015\u0010\u0000\u001a\u00020\u0001*\u00020\u00028F¢\u0006\u0006\u001a\u0004\b\u0003\u0010\u0004¨\u0006\f"},
        d2 = {"size", "", "LAstronomicalBody;", "getSize", "(LAstronomicalBody;)I", "main", "", "args", "", "", "([Ljava/lang/String;)V", "display", "kotlinDee"}
)
public final class ExtensionKt {
   public static final int getSize(@NotNull AstronomicalBody $this$size) {
      Intrinsics.checkParameterIsNotNull($this$size, "$this$size");
      return $this$size.getName().length();
   }

   @NotNull
   public static final String display(@NotNull AstronomicalBody $this$display) {
      Intrinsics.checkParameterIsNotNull($this$display, "$this$display");
      return "Body " + $this$display.getName() + ' ' + getSize($this$display);
   }

   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      Iterable $this$forEach$iv = (Iterable)SolarSystem.INSTANCE.getBodies();
      int $i$f$forEach = false;
      Iterator var3 = $this$forEach$iv.iterator();

      while(var3.hasNext()) {
         Object element$iv = var3.next();
         AstronomicalBody it = (AstronomicalBody)element$iv;
         int var6 = false;
         String var7 = display(it);
         boolean var8 = false;
         System.out.println(var7);
      }

   }
}

Extension

Permet d'enrichir les APIs Java
- Android KTX
- Spring
- RxKotlin
- ...
Permet la SoC (Separation of Concerns)

Les collections

Collections

Les collections

Les Maps

api.kt

val s = SolarSystem.bodies
    .filterIsInstance<Planet>()
    .flatMap { planet -> planet.moons } // 😻
    .filterNot { it.name.startsWith("S/") }
    .sortedBy { it.name }
//        .fold("") { acc, moon ->
//            (if (acc == "") "" else "$acc,\n") + moon.name
//        }
    .joinToString(",\n") { it.name }

println(s)

break-immutable.kt

fun main(args: Array<String>) {
    val moons = (1..9).map { Moon("Moon #$it") }.toList()

    println(moons.javaClass) // class java.util.ArrayList

    moons.javaClass.methods
        .find { it.name == "add" && it.parameterCount == 1 }
        ?.invoke(moons, Moon("XXX"))

    println(moons.joinToString("\n"))
    // Moon(name=Moon #1)
    // Moon(name=Moon #2)
    // Moon(name=Moon #3)
    // Moon(name=Moon #4)
    // Moon(name=Moon #5)
    // Moon(name=Moon #6)
    // Moon(name=Moon #7)
    // Moon(name=Moon #8)
    // Moon(name=Moon #9)
    // Moon(name=XXX)
}

sequence.kt

val s = SolarSystem.bodies.asSequence()
    .filterIsInstance<Planet>()
    .flatMap { planet -> planet.moons.asSequence() } // 😻
    .filterNot { it.name.startsWith("S/") }
    .sortedBy { it.name }
    .joinToString(",\n") { it.name }

println(s)

Performance des séquences 1/2

JMH benchmarks
Benchmark	Mode	Cnt	Score	Error	Units
ApiClassic	thrpt	200	44535.029	3550.944	ops/s
ApiSequence	thrpt	200	23652.238	1967.535	ops/s

ApiClassic 44535 ops/s

44535 ops/s

ApiSequence 23652 ops/s

23652 ops/s

Benchmark séquences 1

sequence2.kt

val s = SolarSystem.bodies.asSequence()
    .filterIsInstance<Planet>()
    .flatMap { planet -> planet.moons.asSequence() } // 😻
    .filterNot { it.name.startsWith("S/") }
    .map { it.name }
    .first()

println(s)

Performance des séquences 2/2

JMH benchmarks
Benchmark	Mode	Cnt	Score	Error	Units
ApiClassicFirst	thrpt	200	241752.062	5022.663	ops/s
ApiSequenceFirst	thrpt	200	3615451.391	454502.198	ops/s

ApiClassicFirst 241752 ops/s

241752 ops/s

ApiSequenceFirst 3615451 ops/s

3615451 ops/s

Benchmark sequences 1

Bilan collection

💪 Super on a de l'immutabilité, des map, flatMap, fold, aggregate,...
🤨 Mais ça reste des collections Java
API standard avec Range, Pair, et Triple
📏 Avant d'utiliser les Sequence, faites des mesures

Les delegates

delegate.kt

import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

fun main(args: Array<String>) {
    val value: String by MyDelegateClass()
    println(value)
}

class MyDelegateClass : ReadOnlyProperty<Nothing?, String> {
    override operator fun getValue(thisRef: Nothing?,
                                   property: KProperty<*>) = "Hello RivieraDev"
}

lazy.kt

object DeepThought {
    fun answer(): Int {
        print("Computing ...")
        return 42
    }
}

fun main() {

    val ultimateQuestionOfLife: Int by lazy {
        DeepThought.answer()
    }
    println("The Ultimate Question of Life, " +
                    "the Universe and Everything ?")
    println("Answer: $ultimateQuestionOfLife" )
}

observable.kt

import kotlin.properties.Delegates

fun main(args: Array<String>) {

    var observable: String by Delegates.observable("Initial value") {
        _, old, new ->
            println("$old -> $new")
    }

    observable = "new value"
}

lateinit.kt

object Plop {
    lateinit var str: String

    fun info() {
        println(Plop::str.isInitialized)
    }
}

fun main() {
    Plop.info() // false
    Plop.str = "Hello"
    Plop.info() // true

    println(str) // Hello
}

Delegate

Lazy : utile pour les propriétés qui ne sont pas systématiquement utilisées.
À manipuler avec précaution dans les activités Android ( avec le cycle de vie, cela peut référencer une ancienne instance)
Delegate : Observable, Not null, ...
lateinit : évite les null check pour les propriétés qui ne peuvent être initialisées immédiatement (ex: référence de vues sur Activity, Fragment).
Ne peut pas être utilisé avec les types primitifs

inline

inline.kt

object Logger {
    var enable: Boolean = false

    inline fun log(msg: () -> String) {
        if (enable) {
            println(msg())
        }
    }
}

fun main() {
    Logger.log { "Hello" }
}

Logger.java

Compiled from "inline-fun.kt"
public final class Inline_funKt {
  public static final void main();
    Code:
       0: getstatic     #15                 // Field Logger.INSTANCE:LLogger;
       3: astore_0
       4: iconst_0
       5: istore_1
       6: aload_0
       7: invokevirtual #19                 // Method Logger.getEnable:()Z
      10: ifeq          27
      13: iconst_0
      14: istore_2
      15: ldc           #21                 // String Hello
      17: astore_2
      18: iconst_0
      19: istore_3
      20: getstatic     #27                 // Field java/lang/System.out:Ljava/io/PrintStream;
      23: aload_2
      24: invokevirtual #33                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      27: nop
      28: return

  public static void main(java.lang.String[]);
    Code:
       0: invokestatic  #9                  // Method main:()V
       3: return
}

reified.kt

class Pojo {
    var name: String? = null
    override fun toString() = "Pojo $name"
}

object JavaBeanBuilder {

    fun <T> createBean(clazz: Class<T>): T =
        clazz.newInstance()

    inline fun <reified T> createBean(): T =
        createBean(T::class.java)
}

fun main(args: Array<String>) {
    val p1 = Pojo()
    p1.name = "Plop1"
    println(p1)

    val p2 = JavaBeanBuilder.createBean<Pojo>()
    p2.name = "Plop2"
    println(p2)
}

reified.java

import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\u0014\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0002\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005¨\u0006\u0006"},
        d2 = {"main", "", "args", "", "", "([Ljava/lang/String;)V", "kotlinDee"}
)
public final class ReifiedKt {
    public static final void main(@NotNull String[] args) {
        Intrinsics.checkParameterIsNotNull(args, "args");
        Pojo p1 = new Pojo();
        p1.setName("Plop1");
        boolean var2 = false;
        System.out.println(p1);
        JavaBeanBuilder this_$iv = JavaBeanBuilder.INSTANCE;
        int $i$f$createBean = false;
        Pojo p2 = (Pojo)this_$iv.createBean(Pojo.class);
        p2.setName("Plop2");
        boolean var6 = false;
        System.out.println(p2);
    }
}

geoloc.kt

inline class Latitude(val value: Double)
inline class Longitude(val value: Double)

data class Geoloc(val lat: Latitude, val lng: Longitude) {

    infix fun distanceTo(other: Geoloc): Double = TODO()
}

fun main() {
    val toulouse = Geoloc(Latitude(43.60426), Longitude(1.44367))
    val nice = Geoloc(Latitude(43.70313), Longitude(7.26608))

    val travel = toulouse distanceTo nice
    println(travel)
}

geoloc bytecode

Compiled from "geoloc.kt"
public final class Geoloc {
  public final double distanceTo(Geoloc);
    Code:
       0: aload_1
       1: ldc           #9                  // String other
       3: invokestatic  #15                 // Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull:(Ljava/lang/Object;Ljava/lang/String;)V
       6: iconst_0
       7: istore_2
       8: new           #17                 // class kotlin/NotImplementedError
      11: dup
      12: aconst_null
      13: iconst_1
      14: aconst_null
      15: invokespecial #21                 // Method kotlin/NotImplementedError."<init>":(Ljava/lang/String;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
      18: checkcast     #23                 // class java/lang/Throwable
      21: athrow

  public final double getLat();
    Code:
       0: aload_0
       1: getfield      #31                 // Field lat:D
       4: dreturn

  public final double getLng();
    Code:
       0: aload_0
       1: getfield      #35                 // Field lng:D
       4: dreturn

  public Geoloc(double, double, kotlin.jvm.internal.DefaultConstructorMarker);
    Code:
       0: aload_0
       1: dload_1
       2: dload_3
       3: invokespecial #42                 // Method "<init>":(DD)V
       6: return
}

Bilan inline

⚠️ les inline, reified, ... sont à manier avec précaution
Inline Functions
⚠️ les inline class sont encore expérimentales
Inline classes

Coroutines

Callback hell problem

fun main(param: Int): Int {
    val step1Result = step1(param)
    return step2(step1Result)
}

Utilisons un callback

fun main(param: Int): Int {
    val step1Result = step1(param)
    return step2(step1Result)
}

`=>`

fun main(param: Int): Int {
    return step1(param) { step1Result ->
        step2(step1Result)
    }

Ajoutons une étape

fun main(param: Int): Int {
    val step1Result = step1(param)
    val step2Result = step2(step1Result)
    return step3Result = step3(step2Result)
}

`=>`

fun main(param: Int): Int {
    return step1(param) { step1Result ->
        step2(step1Result) { step2Result ->
            step3(step2Result)
        }
    }

suspend

suspend fun main(param: Int): Int {
    val step1Result = step1(param)
    val step2Result = step2(step1Result)
    return step3Result = step3(step2Result)
}

Continuation

suspend fun step2(step1Result: Int): Int = TODO()

import kotlin.Metadata;
import kotlin.NotImplementedError;
import kotlin.coroutines.Continuation;
import kotlin.jvm.internal.DefaultConstructorMarker;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

@Metadata(
        mv = {1, 1, 15},
        bv = {1, 0, 3},
        k = 2,
        d1 = {"\u0000\n\n\u0000\n\u0002\u0010\b\n\u0002\b\u0003\u001a\u0019\u0010\u0000\u001a\u00020\u00012\u0006\u0010\u0002\u001a\u00020\u0001H\u0086@ø\u0001\u0000¢\u0006\u0002\u0010\u0003\u0082\u0002\u0004\n\u0002\b\u0019¨\u0006\u0004"},
        d2 = {"step2", "", "step1Result", "(ILkotlin/coroutines/Continuation;)Ljava/lang/Object;", "devoxxfr"}
)
public final class BaseKt {
    @Nullable
    public static final Object step2(int step1Result, @NotNull Continuation $completion) {
        boolean var2 = false;
        throw (Throwable)(new NotImplementedError((String)null, 1, (DefaultConstructorMarker)null));
    }
}

API Continuation

Plus sur les coroutines

Channel (expérimental)
Context
dispatchers
Jobs
Scope

On atteind les limites du décompilateur

Conclusion

Android

Serveur

Supporté officiellement depuis Spring 5, Spring Boot 2
SparkJava, javalin
Vert.x
KTor
...

Web et Natif

🕸 Web

Partager du code commun
Use Kotlin with npm, webpack and react
De l'espoir avec dukat

Natif

Faire des applications sans JVM
Partager du code avec iOS
WebAssembly

Bilan

💎 JVM
😎 Le byte code c'est cool
🔮 Généralement, ça ne suffit pas pour prédire les performances
📏 Mesurez !

Tendance

Stackoverflow trends, et Stackoverflow insights

The State of the Octoverse

Kotlin vs Java

C'est déjà mature
✊ Code plus expressif, plus sûr, plus simple
🤝 Interopérable avec Java
👍 Outillage (éditeur, gradle, maven)
👍 Ecosystème et communauté
🚀 Évolution rapide
🐣 Code multiplatform
Kotlin réussit une belle alchimie entre pragmatisme, puissance, sûreté, accessibilité.

Deep Dive Kotlin : du Hello World au ByteCode

Emmanuel Vinas

Igor Laborie

Introduction

ByteCode Java ?

Introduction Kotlin

Les bases

null-safety

Les types

Les fonctions

Les lambdas

Les classes

Pause

ByteCode Android

Autres structures

Extensions de fonctions

Les collections

Les delegates

inline

Coroutines

Conclusion

ByteCode Java ?

Introduction Kotlin

JVM et Android

JavaScript

Native avec LLVM

Les bases

null-safety

Les types

Les fonctions

Les lambdas

Les classes

Borne supérieure

Pause

ByteCode Android

Autres structures

Extensions de fonctions

Les collections

Les delegates

inline

Deep Dive Kotlin :
du Hello World au ByteCode