kotlinlang #announcements

I want to declare an array but do not want to put values into it then itself I will enter values later when require , as it happens in other languages , however how should I do it in Kotlin

jmfayard

11/05/2019, 10:43 AM

I have colleagues that use

.let { ... }

all the time and don't really understand the need for the others. I know there are multiple articles on when to use

let, also, with, apply, run, takeIf, ...

But which one did you find the most useful?

Exerosis

11/05/2019, 1:30 PM

Compound Extensions... will they exist at some point?

Exerosis

11/05/2019, 1:33 PM

there is some talk here... I totally need them... actually I simply want:

interface SomethingWithEvents {
    fun Toggled.onSomething(listener: () -> (Unit))
}

To get called like this:

fun main(args: Array<String>) {
    (args as Toggled).apply {
        val something = args as SomethingWithEvents
        something.onSomething {
            println("Come on Kotlin for real m8")
        }
    }
}

which would ultimately make a java call like this:

something.onSomething(this, () -> {

});

Vishnu Haridas

11/05/2019, 2:24 PM

How idiomatic is using an Immediately Invoked Function Expression (IIFE) with an Elvis after

let

also

apply

etc. to execute some code when the receiver is null? For example,

val response = getFromUrl(...)

response?.data?.user?.also {
    ...  // welcome the user, save data, and lot more.
} ?: {
    showError("Login failed")
} ()  // IIFE

Iaroslav Postovalov

11/05/2019, 5:13 PM

Hey! Why does mutableMapOf return exactly LinkedHashMap, not a simple HashMap? upd.: I understand why mutableListOf returns ArrayList - it is the most frequently used implementation of MutableList... But why do we need LinkedHashMap? By what criterion is it better than plain HashMap?

➕ 6

Robert Jaros

11/05/2019, 7:17 PM

Anyone knows a library which allows to send email from Kotlin/JVM app without blocking (coroutines? reactive?)

Kroppeb

11/05/2019, 11:39 PM

IntelliJ suggests to convert

r1

r2

, but these are not equivalent. (The inferred type isn't even the same) Seems to be an issue if an extension function on a nullable type gives a generic type with the input type as one of the type parameters and as input a nullable type with a nullable parameter

Mani

11/06/2019, 10:06 AM

val pickableState = try {
            PickableState.valueOf(state)
        } catch (ex: Exception){
            null
        }

is there a better way to check if a string is present in ENUM?

jeggy

11/06/2019, 11:38 AM

I have a big kotlin project that takes about 3-5 minutes to start up using the play button in IntelliJ. So now I wanted to know why it takes so long, so I tried the new Java Flight Recorder to figure what was wrong, and found that nothing was wrong and by using java flight recorder it actually started in 1-3 seconds and everything is working fine. Does anyone know what it could be that I'm doing wrong?

AndreyVanDenHaag

11/06/2019, 3:29 PM

Hi all, I would like to try Ktor to implement a server for a TCP based protocol. All the documentation and examples are about HTTP. The only docs I could find is this: https://ktor.io/servers/raw-sockets.html Can anyone point me to a blog or a project to get more information how to implement non-HTTP protocol with Ktor ?

alex

11/06/2019, 11:07 PM

Right now I'm getting

ClassCastException

and debugging shows that

line no. 12

does nothing. What might be the reason, that

inline

version sometimes (for some calls) skips the cast and returns the same object (i.e.

String

) instead of

reified T

? Classic approach with passing class ref works fine.

Untitled

Raymond Barlow

11/07/2019, 4:41 AM

is there a `const()`funciton in Kotlin? (or equivalent)

vineethraj49

11/07/2019, 6:08 AM

does

!==

just translate to

!  ==

which is

!=

Roberto Messina

11/07/2019, 9:23 AM

How can i clear intellij console by kotlin?

Oleh Ponomarenko

11/07/2019, 11:25 AM

How can I transalte this to Kotlin from Java:

while ((inputLine = input.readLine()) != null) {
Log.d(TAG, inputLine);
   }

Jakub Begera

11/07/2019, 11:47 AM

Hello, I’m dealing with following issue with Kotlin/Java Compiler. Imagine following scenario: let

First

be a Java class with a final function and

Second

be a Kotlin class extending

First

with a function of the same name like the final function in

First

class, i. e.:

// Java class
class Firs {
    final void foo() { }
}

// Kotlin class
class Second: First() {
    fun foo() { }
}

Obviously, it’s wrong because the final function

foo()

can not be overridden. However, compilation pass successfully and in run-time I get

java.lang.LinkageError: Method void Second.foo() overrides final method in class First

. Is this correct behavior of compiler? I supposed that there will be some validations for this case. Thank you! 🙂

😬 2

:yes: 1

LeoColman

11/07/2019, 3:35 PM

But I don't really want to, I want it to cast everything to Any if the user doesn't provide the value

Ellen Spertus

11/07/2019, 8:20 PM

How would I fix this code? I’d like

reportError()

to be called if the value preceding

let

is `null`:

store.state.selectedTab?.content?.url.let {
     doSomething(it)
 } ?: run {
     reportError("Unable to get URL to send")
 }

Assume that both

doSomething()

and

reportError()

are void.

Brian Norman

11/08/2019, 1:15 AM

In Kotlin how do you test equivalence between two Lists? i.e content is the same but not necessarily the same order?

Antonio Aradaza

11/08/2019, 1:38 AM

Hello, how to call a function at the start of application then stop it immediately? Like "one-time" use only

John

11/08/2019, 12:14 PM

Other than making it "work" with vararg that is

nimtiazm

11/08/2019, 8:41 PM

In multiline string, is there a way to add newline in literal but not in string itself? I realize it’s possible to do

""" …\n """.replace("\n", "")

but i’m looking for a better way

Hullaballoonatic

11/09/2019, 5:01 AM

What is the point of

ByteArray

IntArray

CharArray

etc? why not just

Array<Byte>

Array<Int>

Array<Char>

. I know that Java does treat primitive arrays differently from object arrays, but couldn't Kotlin do us a solid and smoosh them all into just

Array<T>

ventura

11/09/2019, 10:39 AM

I am trying to create scaffolding script for creating Ktor apps from CLI (like Django, Rails, etc). Should I use Yeoman (i.e. write in JavaScript) or is there a more Kotlin-way of doing it?

hellman

11/09/2019, 4:05 PM

I got this at the moment, but that doesn’t work:

plugins {
    id("org.jetbrains.kotlin.js") version "1.3.60-eap-76"
}

repositories {
    mavenCentral()
    mavenLocal()
    maven(url = "<https://dl.bintray.com/kotlin/kotlin-eap>")
}

william

11/10/2019, 3:57 AM

since there are no checked exceptions in kotlin, is it best to have error return values instead?

Travis Griggs

11/10/2019, 5:13 AM

I have a typealias for UInt (

typealias PlanOID = UInt

). Ideally, I’d like to bind a class/type/static function to PlanOID (e.g.

PlanOID.nowOID()

), but I think this is not possible. I’m assuming that PlanOID is just what it says, a substitution alias, not a distinct type. And since UInt doesn’t have a Companion, I can’t extend that. Is this correct? Am I missing some other trick. I get that I can just define a global free function, but I’d rather bind the behavior to the type if I could (avoids namespace clutter)

Marcin Wisniowski

11/10/2019, 11:49 AM

Does anyone have an idiomatic way of checking if the last

elements of a list are the same? Currently I have

list.takeLast(n).toSet().size == 1

but I think this could be simpler.

zceejkr

11/10/2019, 4:34 PM

Hi, one question if I may: I have a sealed class Foo that is extended by A, B and C and a generic interface Bar<T>. Bar only requires one method that returns T. I want to make an object of type Bar<Foo>, that will return one of the Foo members. But if I put the type Bar<Foo> and try to return A in the required method, I get a type error (it wants Foo, not A). If I put the type Bar<out Foo>, i get this error:

Projections are not allowed for immediate arguments of a supertype

. I am new to generics so if anyone can point me in the right direction I would be thankful.

Title

zceejkr

11/10/2019, 4:34 PM

Projections are not allowed for immediate arguments of a supertype

. I am new to generics so if anyone can point me in the right direction I would be thankful.

streetsofboston

11/10/2019, 4:38 PM

Did you try to declare Bar as follows, with a covariant generic param

(out on the declaration site):

interface Bar<out T> { fun oneMethodThatReturnsT(): T }

Also, if you could provide a snippet of the code that doesn’t compile would really help 🙂

zceejkr

11/10/2019, 6:17 PM

Ok so I have done so and it works now (on JVM). But the same code does not work when compiled to JavaScript. Not a compile time error, it does not work at runtime. The example is somewhat convoluted and I think it might be a bug with kotlinc-js. Do you know where I could report such a bug?

karelpeeters

11/10/2019, 7:21 PM

https://youtrack.jetbrains.com/oauth?state=%2Fissues%2FKT

👍 1

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