There's No Magic - How Kotlin can be your best friends @DevFest LA 2017

Kotlin finally got official support from Google. While a lot of people are cheering, some are hesitating. Should I use it in production? What are all those fancy features? How is Kotlin able to do that? In this talk, I'll share my experience with Kotlin and go a little bit in detail on what Kotlin is doing under the hood.

Transcript

1. There’s no magic - How Kotlin can be your best friend Aaron He
2. Kotlin@Tinder
3. Kotlin@Tinder • First APK shipped with Kotlin in June • Our app has ~32% Kotlin adoption • Developers are happy
4. How did we get here?
5. inline functions property reified higher-order functions immutable collections extension functions companion object Any object object no NPEs delegation data class sealed class in and out coroutines internal visibility type aliases Java interop by lazy lateinit
7. Compilation process *.java javac *.class *.dex dex *.kt kotlinc
8. Configuration for Gradle https://kotlinlang.org/docs/tutorials/kotlin-android.html
9. Nullabiltity
10. class Location(var street: String?, var city: String?) class Conference(var name: String?, var location: Location?) fun printCity(conference: Conference?) { println(conference?.location?.city) }
11. Huh?
13. Ok. Sure!
14. // access flags 0x2 private Ljava/lang/String; name @Lorg/jetbrains/annotations/Nullable;() // invisible // access flags 0x11 public final getName()Ljava/lang/String; @Lorg/jetbrains/annotations/Nullable;() // invisible L0 LINENUMBER 4 L0 ALOAD 0 GETFIELD org/aaronhe/Conference.name : Ljava/lang/String; ARETURN L1 LOCALVARIABLE this Lorg/aaronhe/Conference; L0 L1 0 MAXSTACK = 1 MAXLOCALS = 1 // access flags 0x11 public final setName(Ljava/lang/String;)V @Lorg/jetbrains/annotations/Nullable;() // invisible, parameter 0 L0 LINENUMBER 4 L0 ALOAD 0 ALOAD 1 PUTFIELD org/aaronhe/Conference.name : Ljava/lang/String; RETURN L1 LOCALVARIABLE this Lorg/aaronhe/Conference; L0 L1 0 LOCALVARIABLE <set-?> Ljava/lang/String; L0 L1 1 MAXSTACK = 2 MAXLOCALS = 2 // access flags 0x2 private Lorg/aaronhe/Location; location @Lorg/jetbrains/annotations/Nullable;() // invisible // access flags 0x11 public final getLocation()Lorg/aaronhe/Location; @Lorg/jetbrains/annotations/Nullable;() // invisible L0 LINENUMBER 4 L0 ALOAD 0 GETFIELD org/aaronhe/Conference.location : Lorg/aaronhe/Location; ARETURN L1 LOCALVARIABLE this Lorg/aaronhe/Conference; L0 L1 0 MAXSTACK = 1 MAXLOCALS = 1 // access flags 0x11 public final setLocation(Lorg/aaronhe/Location;)V @Lorg/jetbrains/annotations/Nullable;() // invisible, parameter 0 L0 LINENUMBER 4 L0 ALOAD 0 EXACTLY!
16. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
17. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
18. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
19. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
20. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
21. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
22. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
23. // DevFest.java package org.aaronhe; import kotlin.Metadata; import org.jetbrains.annotations.Nullable; @Metadata( mv = {1, 1, 7}, bv = {1, 0, 2}, k = 1, d1 = {"\u0000\u0018\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0000\u0018\u0000 2\u00020\u0001B\u0005¢ \u0006\u0002\u0010\u0002J\u0010\u0010\u0003\u001a\u00020\u00042\b\u0010\u0005\u001a\u0004\u0018\u00010\u0006¨\u0006\u0007"}, d2 = {"Lorg/aaronhe/DevFest;", "", "()V", "printCity", "", "conference", "Lorg/aaronhe/Conference;", "production sources for module moshi-kotlin"} ) public final class DevFest { public final void printCity(@Nullable Conference conference) { String var3; label12: { if (conference != null) { Location var10000 = conference.getLocation(); if (var10000 != null) { var3 = var10000.getCity(); break label12; } } var3 = null; } String var2 = var3; System.out.println(var2); } }
24. Extension methods
25. fun Conference.isInLA():Boolean { return this.location?.city == "Los Angeles" }
26. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
27. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
28. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
29. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
30. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
31. public final class ConferenceExtKt { public static final boolean isInLA(@NotNull Conference $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); Location var10000 = $receiver.getLocation(); return Intrinsics.areEqual(var10000 != null ? var10000.getCity() : null, "Los Angeles"); } }
32. // What is this Java thing? public boolean checkIfInLA(@NotNull Conference conference) { return ConferenceExtKt.isInLA(conference); }
33. Kotlin standard library public char lastCharacter(@NotNull String string) { return StringsKt.last(string); } public <T, R> List<R> map(@NotNull List<T> list, Function1<T, R> mapper) { return CollectionsKt.map(list, mapper); }
34. Data class
35. class Conference(var name: String?, var location: Location?)
36. data class Conference(var name: String?, var location: Location?)
37. public int hashCode() { return (this.name != null ? this.name.hashCode() : 0) * 31 + (this.location != null ? this.location.hashCode() : 0); } public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Conference) { Conference var2 = (Conference)var1; if (Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.location, var2.location)) { return true; } } return false; } else { return true; } }
38. public int hashCode() { return (this.name != null ? this.name.hashCode() : 0) * 31 + (this.location != null ? this.location.hashCode() : 0); } public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Conference) { Conference var2 = (Conference)var1; if (Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.location, var2.location)) { return true; } } return false; } else { return true; } }
39. public int hashCode() { return (this.name != null ? this.name.hashCode() : 0) * 31 + (this.location != null ? this.location.hashCode() : 0); } public boolean equals(Object var1) { if (this != var1) { if (var1 instanceof Conference) { Conference var2 = (Conference)var1; if (Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.location, var2.location)) { return true; } } return false; } else { return true; } }
40. public String toString() { return "Conference(name=" + this.name + ", location=" + this.location + ")"; }
41. @NotNull public final Conference copy(@Nullable String name, @Nullable Location location) { return new Conference(name, location); }
42. Immutability
43. @Nullable public final String getName() { return this.name; } public final void setName(@Nullable String var1) { this.name = var1; } @Nullable public final Location getLocation() { return this.location; } public final void setLocation(@Nullable Location var1) { this.location = var1; }
44. data class Conference(val name: String, val location: Location)
45. @NotNull private final String name; @NotNull private final Location location; @NotNull public final String getName() { return this.name; } @NotNull public final Location getLocation() { return this.location; }
46. @NotNull private final String name; @NotNull private final Location location; @NotNull public final String getName() { return this.name; } @NotNull public final Location getLocation() { return this.location; }
47. @NotNull private final String name; @NotNull private final Location location; @NotNull public final String getName() { return this.name; } @NotNull public final Location getLocation() { return this.location; }
48. See the decompiled Bytecode to uncover
49. Thank you! @aaronhe42 aaronhe42@gmail.com Tinder is hiring: https://www.gotinder.com/jobs