Exploration of how Kotlin 1.4 optimizes compilation of lazy as delegated property

How Kotlin 1.4 optimizes compilation of lazy and how to use it in Kotlin 1.3

Preconditions

• kotlin 1.4M1 (how to try)
• kotlin 1.3.X
• gradle 5+ (Kotlin DSL is used in build.gradle.kts)
• javap
• procyon

Source Code

clean

./gradlew clean

compile

./gradlew build

run

./gradlew run

decompile

cd build/classes/kotlin/main/info/lotharschulz/lazy && procyon Dearlazy && cd ../../../../../../..
# does return different results than:
# procyon build/classes/kotlin/main/info/lotharschulz/lazy/Dearlazy

# two commands below show the same result
javap -c -p build/classes/kotlin/main/info/lotharschulz/lazy/Dearlazy
cd build/classes/kotlin/main/info/lotharschulz/lazy/ && javap -c -p Dearlazy && cd ../../../../../../..

test

./gradlew test

key commands one liner

./gradlew clean test run && cd build/classes/kotlin/main/info/lotharschulz/lazy/ && procyon Dearlazy && cd ../../../../../../..

I am happy about your contributions ☺️.

Links

• https://youtu.be/MYQWtNG2so8?list=LLaVcONSNkhDcKwqzpYHUajA&t=150

• https://youtu.be/MYQWtNG2so8?list=LLaVcONSNkhDcKwqzpYHUajA&t=177

• https://youtu.be/MYQWtNG2so8?list=LLaVcONSNkhDcKwqzpYHUajA&t=1527

• https://blog.jetbrains.com/kotlin/2019/12/what-to-expect-in-kotlin-1-4-and-beyond/#delegated-properties

  • https://blog.jetbrains.com/kotlin/2019/12/what-to-expect-in-kotlin-1-4-and-beyond/#trailing-commas

• https://javahungry.blogspot.com/2018/12/8-best-java-decompiler-in-2019.html

Decompiled classes

kotlin version 1.4-M1

$ ./gradlew clean test run && cd build/classes/kotlin/main/info/lotharschulz/lazy/ && procyon Dearlazy && cd ../../../../../../..

> Task :run
hi

BUILD SUCCESSFUL in 2s
3 actionable tasks: 3 executed
// 
// Decompiled by Procyon v0.5.32
// 

package info.lotharschulz.lazy;

import kotlin.LazyKt;
import kotlin.jvm.functions.Function0;
import kotlin.LazyThreadSafetyMode;
import org.jetbrains.annotations.NotNull;
import kotlin.Lazy;
import kotlin.Metadata;

@Metadata(mv = { 1, 4, 0 }, bv = { 1, 0, 3 }, k = 1, xi = 2, d1 = { "\u0000\u0014\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0005\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002R\u001b\u0010\u0003\u001a\u00020\u00048FX\u0086\u0084\u0002¢\u0006\f\n\u0004\b\u0007\u0010\b\u001a\u0004\b\u0005\u0010\u0006¨\u0006\t" }, d2 = { "Linfo/lotharschulz/lazy/Dearlazy;", "", "()V", "myLazyString", "", "getMyLazyString", "()Ljava/lang/String;", "myLazyString$delegate", "Lkotlin/Lazy;", "lazy" })
public final class Dearlazy
{
    @NotNull
    private final Lazy myLazyString$delegate;
    
    @NotNull
    public final String getMyLazyString() {
        return (String)this.myLazyString$delegate.getValue();
    }
    
    public Dearlazy() {
        this.myLazyString$delegate = LazyKt.lazy(LazyThreadSafetyMode.SYNCHRONIZED, (Function0)Dearlazy$myLazyString.Dearlazy$myLazyString$2.INSTANCE);
    }
}

kotlin version 1.3.70

$ ./gradlew clean test run && cd build/classes/kotlin/main/info/lotharschulz/lazy/ && procyon Dearlazy && cd ../../../../../../..

> Task :run
hi

BUILD SUCCESSFUL in 18s
3 actionable tasks: 3 executed
// 
// Decompiled by Procyon v0.5.32
// 

package info.lotharschulz.lazy;

import kotlin.LazyKt;
import kotlin.jvm.functions.Function0;
import kotlin.LazyThreadSafetyMode;
import org.jetbrains.annotations.NotNull;
import kotlin.Lazy;
import kotlin.Metadata;

@Metadata(mv = { 1, 1, 16 }, bv = { 1, 0, 3 }, k = 1, d1 = { "\u0000\u0014\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0005\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002R\u001b\u0010\u0003\u001a\u00020\u00048FX\u0086\u0084\u0002¢\u0006\f\n\u0004\b\u0007\u0010\b\u001a\u0004\b\u0005\u0010\u0006¨\u0006\t" }, d2 = { "Linfo/lotharschulz/lazy/Dearlazy;", "", "()V", "myLazyString", "", "getMyLazyString", "()Ljava/lang/String;", "myLazyString$delegate", "Lkotlin/Lazy;", "lazy" })
public final class Dearlazy
{
    @NotNull
    private final Lazy myLazyString$delegate;
    
    @NotNull
    public final String getMyLazyString() {
        return (String)this.myLazyString$delegate.getValue();
    }
    
    public Dearlazy() {
        this.myLazyString$delegate = LazyKt.lazy(LazyThreadSafetyMode.SYNCHRONIZED, (Function0)Dearlazy$myLazyString.Dearlazy$myLazyString$2.INSTANCE);
    }
}

kotlin version 1.3.61

$ ./gradlew clean test run && cd build/classes/kotlin/main/info/lotharschulz/lazy/ && procyon Dearlazy && cd ../../../../../../..

> Task :run
hi

BUILD SUCCESSFUL in 2s
3 actionable tasks: 3 executed
// 
// Decompiled by Procyon v0.5.32
// 

package info.lotharschulz.lazy;

import kotlin.LazyKt;
import kotlin.jvm.functions.Function0;
import kotlin.LazyThreadSafetyMode;
import kotlin.jvm.internal.PropertyReference1;
import kotlin.reflect.KDeclarationContainer;
import kotlin.jvm.internal.PropertyReference1Impl;
import kotlin.jvm.internal.Reflection;
import org.jetbrains.annotations.NotNull;
import kotlin.Lazy;
import kotlin.reflect.KProperty;
import kotlin.Metadata;

@Metadata(mv = { 1, 1, 16 }, bv = { 1, 0, 3 }, k = 1, d1 = { "\u0000\u0014\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0005\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002R\u001b\u0010\u0003\u001a\u00020\u00048FX\u0086\u0084\u0002¢\u0006\f\n\u0004\b\u0007\u0010\b\u001a\u0004\b\u0005\u0010\u0006¨\u0006\t" }, d2 = { "Linfo/lotharschulz/lazy/Dearlazy;", "", "()V", "myLazyString", "", "getMyLazyString", "()Ljava/lang/String;", "myLazyString$delegate", "Lkotlin/Lazy;", "lazy" })
public final class Dearlazy
{
    static final /* synthetic */ KProperty[] $$delegatedProperties;
    @NotNull
    private final Lazy myLazyString$delegate;
    
    static {
        $$delegatedProperties = new KProperty[] { (KProperty)Reflection.property1((PropertyReference1)new PropertyReference1Impl((KDeclarationContainer)Reflection.getOrCreateKotlinClass((Class)Dearlazy.class), "myLazyString", "getMyLazyString()Ljava/lang/String;")) };
    }
    
    @NotNull
    public final String getMyLazyString() {
        final Lazy myLazyString$delegate = this.myLazyString$delegate;
        final KProperty kProperty = Dearlazy.$$delegatedProperties[0];
        return (String)myLazyString$delegate.getValue();
    }
    
    public Dearlazy() {
        this.myLazyString$delegate = LazyKt.lazy(LazyThreadSafetyMode.SYNCHRONIZED, (Function0)Dearlazy$myLazyString.Dearlazy$myLazyString$2.INSTANCE);
    }
}