kotlinlang #getting-started

I recently discovered on a project that at least on Android, creating a new Timer is equivalent co creating a new Thread, so you would probably want to have a threadpool or something you are dispatching to rather than creating a new Timer every time the method is called (depending on how frequently the method is called, of course).

witoldsz

06/11/2017, 10:39 PM

Strange things: Kotlin complains that my function has a parameter that is never used. What am I supposed to do with this warning? My function must have it declared or it won't comply to the interface. The compiler should not add a noise with such a useless warning.

jasonlow

06/12/2017, 2:12 AM

and to begin with, how do I even write the expression to init the enum class?

Color("red")

does not work because

enum types cannot be instantiated

. And

Color.valueof("red")

throws me an

illegal argument exception

sk0g

06/12/2017, 12:34 PM

Hey so, I don't have any Android experience yet, but I have done an intro to programming in Java and am currently in second year of Software Engineering. How hard would it be to get into making Android apps without much, if any, Java?

Ruckus

06/12/2017, 3:03 PM

You can use something like

enum class People(value: Int) {
    man(1),
    baby(2),
    woman(3);

    companion object {
        fun byValue(value: Int) = values().firstOrNull { it.value == value }
    }
}

val people = People.byValue(3)
if (people != null) {
    print("converted successfully => $people")
} else {
    print("null value -> No Match")
}

tulio

06/12/2017, 4:22 PM

Thanks for the answers, I think I will stick with the if version 🙂

👍 1

cedric

06/12/2017, 4:33 PM

@tulio A few thoughts here: http://beust.com/weblog/2016/01/14/a-close-look-at-kotlins-let/ tldr: I tend to stick to

if

cedric

06/13/2017, 4:14 PM

@mmaillot No,

Result

is not a monad, it lacks a few things for that.

igor.wojda

06/13/2017, 11:44 PM

Hey can somebody give me proper example why val may be not initialized at compile time (so we need to add

const

modifier) ?

kingvhit

06/14/2017, 2:45 AM

Sorry for my stupid question but does anybody let me know how can import synthetic automatically ? Like :

import kotlinx.android.synthetic.main.activity_main.*

Or any shortcut do it by your hand ?

alvico

06/14/2017, 8:39 AM

hey does anyone know about expert and good Kotlin teaches willing to give courses to interpresises in europe?

gildor

06/14/2017, 9:36 AM

@jasonlow There is firstOrNull if you want to get nullable value. Reason - you can use

first

and get nonnull result

angloha

06/14/2017, 4:52 PM

Please i need book to learn Kotlin

darger

06/14/2017, 7:32 PM

Hello - I am trying to get started with Kotlin. I tried to download the command-line compiler - wget the download link on https://github.com/JetBrains/kotlin/releases/tag/v1.1.2-5 - it redirects to an obscure place on S3. All is probably fine but is it not possible to verify the integrity of the release in any way? Preferably via a GPG signature, alternatively via a SHA-2 digest?

akperkins1

06/14/2017, 8:10 PM

Hey guys, I want to learn Kotlin by contributing to some popular open source libraries on github. Does anyone have any suggestions?

witoldsz

06/14/2017, 9:58 PM

Hello! What is the easiest way to make Idea show me sources of Kotlin stdlibs? I was hoping the plugin will figure it out, but as of now all I can see are the signatures and

Decompile to Java

Choose sources

. Should I download sources, unpack, point to Idea or the sources should be already somewhere? I am building project using Gradle, no cmd-line tools or other stuff installed.

punitjajo

06/15/2017, 4:15 AM

I’m building an online compiler for C, Python and Kotlin. C and Python work well, but Kotlin compilation takes a long time. Any feedback on how I can make the compilation faster? http://52.170.87.157:8079/kotlin.html

elect

06/15/2017, 10:31 AM

if I rewrite this

fun findWindowSettings(name:String): IniData? {
    val id = hash(name, 0)
    return g.settings.firstOrNull { it.id == id }
}

fun findWindowSettings(name:String) = g.settings.firstOrNull { it.id == hash(name, 0) }

will be the

hash()

result cached or executed each time?

duncanconroy

06/15/2017, 2:16 PM

Hi there, I'm new to Kotlin and currently writing a text file parser. I've come across the useful function File.forEachLine. What I want to do know, is to print out the progress of file reading, e.g. by getting the current file pointer. It seems that I can neither access the InputStream, which is used inside the forEachLine function, nor can I find another way of getting the current position in the file. Does someone know how I can get file position or currentLine / totalLines within forEachLine? Thanks in advance!

ishwerdas

06/15/2017, 3:21 PM

I am javascript developer, never worked in java.. and hence never worked on android development through traditional means ... any tips on how should I go about learning kotlin?

mmaillot

06/15/2017, 4:02 PM

I don't see the channel, thank you, i'll try that!

chuck

06/15/2017, 4:33 PM

For example, there are no implicit widening conversions for numbers ...

Why not? https://kotlinlang.org/docs/reference/basic-types.html https://kotlinlang.org/docs/reference/basic-types.html#explicit-conversions

daveroberts

06/15/2017, 5:20 PM

I'm looking at the Hello World build.gradle file. https://github.com/JetBrains/kotlin-examples/blob/master/gradle/hello-world/build.gradle I noticed that repositories and dependencies are listed twice, once in the buildScript and once in the root. Is there any documentation for why there are two? When I want to add a new dependency, does it need to go in one or both?

bryan

06/16/2017, 5:40 AM

case VALIDATE_PAIRING_KEY

evkaky

06/16/2017, 8:09 AM

guys, tail recursion is a so tasty optimization. Why it’s not turned on by default in kotlin? Why compiler can’t itself to recognize all cases for tail recursions in our code, and do appropirate stuff? Why do we need manually tolk to compiler via special keyword? (like “tailrec”). Tail recursion seems to be an ordinary optimization, like constant folding… and kotlin (and other langs) have no special keywords to turn constant folding optmiziations on!

thecipster

06/16/2017, 10:54 AM

Hi! I want to do something if a

java.io.File

variable is null or not readable. In Java this vould be

if (myFile == null || !myFile.canRead()) {
    // error!
}

which works always because of short-circuit evaluation. IntelliJ translates the above code to:

if (simDesc == null || !simDesc!!.canRead()) {
    // error!
}

which is a bit ugly IMHO. Any idea on making it more idiomatic?

voddan

06/16/2017, 11:40 AM

Maybe you want to use an

if

inside the

when

is String -> if("HELLO".equals(obj.toUpperCase()))) println("Greeting")

ktw

06/16/2017, 1:21 PM

I installed 1.1.3 EAP in Intellij, but now the REPL keeps freezing. Any way to get back to 1.1.2?

perryprog

06/16/2017, 3:35 PM

Jun 16, 2017 11:34:03 AM org.junit.platform.launcher.core.ServiceLoaderTestEngineRegistry loadTestEngines
INFO: Discovered TestEngines with IDs: [spek]
Exception in thread "main" java.lang.AbstractMethodError: Method org/jetbrains/spek/engine/Scope$Group.isTest()Z is abstract
	at org.jetbrains.spek.engine.Scope$Group.isTest(Scope.kt)
	at org.junit.platform.engine.TestDescriptor.hasTests(TestDescriptor.java:160)
	at org.junit.platform.launcher.core.Root.lambda$static$0(Root.java:33)
	at org.junit.platform.engine.TestDescriptor.accept(TestDescriptor.java:179)
	at org.junit.platform.engine.TestDescriptor.lambda$accept$0(TestDescriptor.java:181)
	at java.lang.Iterable.forEach(Iterable.java:75)
	at org.junit.platform.engine.TestDescriptor.accept(TestDescriptor.java:181)
	at org.junit.platform.launcher.core.Root.lambda$acceptInAllTestEngines$2(Root.java:85)
	at java.util.LinkedHashMap$LinkedValues.forEach(LinkedHashMap.java:608)
	at org.junit.platform.launcher.core.Root.acceptInAllTestEngines(Root.java:85)
	at org.junit.platform.launcher.core.Root.prune(Root.java:77)
	at org.junit.platform.launcher.core.DefaultLauncher.discoverRoot(DefaultLauncher.java:117)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:85)
	at org.jetbrains.spek.tooling.runner.junit.JUnitPlatformSpekRunner.run(JUnitPlatformSpekRunner.kt:107)
	at org.jetbrains.spek.tooling.MainKt.main(Main.kt:58)

Title

perryprog

06/16/2017, 3:35 PM

Jun 16, 2017 11:34:03 AM org.junit.platform.launcher.core.ServiceLoaderTestEngineRegistry loadTestEngines
INFO: Discovered TestEngines with IDs: [spek]
Exception in thread "main" java.lang.AbstractMethodError: Method org/jetbrains/spek/engine/Scope$Group.isTest()Z is abstract
	at org.jetbrains.spek.engine.Scope$Group.isTest(Scope.kt)
	at org.junit.platform.engine.TestDescriptor.hasTests(TestDescriptor.java:160)
	at org.junit.platform.launcher.core.Root.lambda$static$0(Root.java:33)
	at org.junit.platform.engine.TestDescriptor.accept(TestDescriptor.java:179)
	at org.junit.platform.engine.TestDescriptor.lambda$accept$0(TestDescriptor.java:181)
	at java.lang.Iterable.forEach(Iterable.java:75)
	at org.junit.platform.engine.TestDescriptor.accept(TestDescriptor.java:181)
	at org.junit.platform.launcher.core.Root.lambda$acceptInAllTestEngines$2(Root.java:85)
	at java.util.LinkedHashMap$LinkedValues.forEach(LinkedHashMap.java:608)
	at org.junit.platform.launcher.core.Root.acceptInAllTestEngines(Root.java:85)
	at org.junit.platform.launcher.core.Root.prune(Root.java:77)
	at org.junit.platform.launcher.core.DefaultLauncher.discoverRoot(DefaultLauncher.java:117)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:85)
	at org.jetbrains.spek.tooling.runner.junit.JUnitPlatformSpekRunner.run(JUnitPlatformSpekRunner.kt:107)
	at org.jetbrains.spek.tooling.MainKt.main(Main.kt:58)

06/16/2017, 3:42 PM

perryprog: it's best to direct these questions on #spek

perryprog

06/16/2017, 3:42 PM

I didn’t know that existed, thanks!

06/16/2017, 3:43 PM

this issue is: https://github.com/JetBrains/spek/issues/195#issuecomment-300645464 basically you need to add:

testRuntime 'org.junit.platform:junit-platform-launcher:1.0.0-M4'

perryprog

06/16/2017, 3:44 PM

Thanks again!

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