What is the intended meaning of “companion object”? Why is it called “companion”? First, Kotlin doesn’t use the Java concept of static members because Kotlin has its own concept of objects for describing properties and functions connected with singleton state, and Java static part of a class can be elegantly expressed in terms of singleton: … Read more
This is one of my favourite things to fix in Gradle, and really shows off the flexibility that’s possible (as well as demonstrating why Gradle can be complicated!) First I’ll give a bit of background info on the subprojects {} DSL, then I’ll show how to fix your script, and finally I’ll show the best … Read more
In Kotlin, if statements are expressions. So the following code is equivalent: if (a) b else c The distinction between expression and statement is important here. In Java/C#/JavaScript, if forms a statement, meaning that it does not resolve to a value. More concretely, you can’t assign it to a variable. // Valid Kotlin, but invalid … Read more
I came accross this answer while having the same issue with Kotlin and gradle. I wanted to package to get the jar to work but kept on pilling errors. With a file like com.example.helloworld.kt containing your code: fun main(args: Array<String>) { println(“Hello, World!”) } So here is what the file build.gradle.kts would look like to … Read more
Quick answer block: SCRIPT.() -> Unit = {} This represents a “function literal with receiver”. It’s a function parameter with a function type () -> Unit and SCRIPT as it’s receiver. Function Literals/Lambda with Receiver Kotlin supports the concept of “function literals with receivers”. It enables the access on visible methods and properties of a … Read more
Actually Kotlin knows the difference between the two methods in your example, but jvm will not. That’s why it’s a “platform” clash. You can make your second example compile by using the @JvmName annotation: class Foo { @JvmName(“barString”) fun bar(foo: List<String>): String { return “” } @JvmName(“barInt”) fun bar(foo: List<Int>): String { return “2”; } … Read more
The issue is most likely that you forgot to depend on the reflection libraries which were needed for the reflective functions of Kotlin. On the Java platform, the runtime component required for using the reflection features is distributed as a separate JAR file (kotlin-reflect.jar). This is done to reduce the required size of the runtime … Read more
This is a bug in the compiler, feel free to vote / watch it: https://youtrack.jetbrains.com/issue/KT-2780
Here is a function to read a property from an instance of a class given the property name (throws exception if property not found, but you can change that behaviour): import kotlin.reflect.KProperty1 import kotlin.reflect.full.memberProperties @Suppress(“UNCHECKED_CAST”) fun <R> readInstanceProperty(instance: Any, propertyName: String): R { val property = instance::class.members // don’t cast here to <Any, R>, it … Read more
Add the plugin application, then set the mainClassName as mainClassName=”[your_namespace].[your_arctifact]Kt” For instance, suppose you have placed the following code in a file named main.kt: package net.mydomain.kotlinlearn import kotlin import java.util.ArrayList fun main(args: Array<String>) { println(“Hello!”) } your build.gradle should be: apply plugin: ‘kotlin’ apply plugin: ‘application’ mainClassName = “net.mydomain.kotlinlearn.MainKt” In fact Kotlin is building a … Read more