@marley 21 May 2020 edited

Kotlin from the ground up, Part 2 - the REPL

In part 1 you set up a barebones command-line Kotlin environment with proper `PATH` settings and learned how to compile Kotlin source into a runnable `.class` or `.jar` file. Now, let's explore the interactive REPL. Invoke as below: https://read.cash/@marley/kotlin-from-the-ground-up-part-1-setup-compile-jar-package-ec4512a2 > kotlinc Welcome to Kotlin version 1.3.72 (JRE 1.8.0_181-b13) Type :help for help, :quit for quit >>> and let's try a few cool & useful things such as how to check what a Kotlin object's class is via reflection : https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect/-k-class/ >>> System.getProperties() res0: java.util.Properties! = { .... ..... } /* What type of object is this returning? */ >>> val sp = System.getProperties() /* It's not a string, it's a Properties object */ >>> sp::class.simpleName res1: kotlin.reflect.KClass<out java.util.Properties!> = class java.util.Properties /* Compare to an integer */ >>> val x = 5 >>> x::class res3: kotlin.reflect.KClass<out kotlin.Int> = class kotlin.Int /* You can reflect directly on literals, not just variables */ >>> 42::class res4: kotlin.reflect.KClass<out kotlin.Int> = class kotlin.Int >>> "hello there"::class res5: kotlin.reflect.KClass<out kotlin.String> = class kotlin.String /* What members does the class provide? Let's make a helper function to show them properly */ >>> fun listMembers(x:Any) { println(); for (m in x::class.members) println(m) } >>> listMembers("I'm a string") val kotlin.String.length: kotlin.Int fun kotlin.String.compareTo(kotlin.String): kotlin.Int fun kotlin.String.get(kotlin.Int): kotlin.Char fun kotlin.String.plus(kotlin.Any?): kotlin.String fun kotlin.String.subSequence(kotlin.Int, kotlin.Int): kotlin.CharSequence fun kotlin.String.chars(): java.util.stream.IntStream! fun kotlin.String.codePoints(): java.util.stream.IntStream! fun kotlin.String.equals(kotlin.Any?): kotlin.Boolean fun kotlin.String.hashCode(): kotlin.Int fun kotlin.String.toString(): kotlin.String I might add more REPL stuff to do here, but for now, you can head on to Part 3 where you finally build a GUI app using Kotlin and the TornadoFX framework! https://read.cash/@marley/kotlin-from-the-ground-up-part-3-creating-a-gui-app-4f6872be