can anyone recommend any good kotlin books or resources for already experienced programmers? i don't want someone to teach me what is if/else, i would like to get a good overview of existing language features and patterns

EDIT: Answered in thread. Could someone please explain, why i can’t access anonymous object’s property, unless I declare val as private? Thank you for your time.

class Demo {
    class Normal {
        val greeting = "I'm Normal class instance"
    }
    val normal = Normal()

    private val privateAnonymous = object {
        val greeting = "I'm anonymous class instance"
    }
    
    val anonymous = object {
        val greeting = "I'm also anonymous class instance"
    }
    
    val normalGreeting = normal.greeting // I'm Normal class instance
    val privateAnonymousGreeting = privateAnonymous.greeting // I'm anonymous class instance
    val anonymousGreeting = anonymous.greeting // Unresolved reference: greeting
}

is there some nice small lib for dealing with byte dimensions (ie: MB, GB)?

Hello, I've spent so much time without managing to get any response: Given a

Kfunction

obtained from an expression such as

obj::method

where obj is an instance from a Class. How can I retrieve the underlying

obj

from the

Kfunction

???

If I have a rather large

Map<String, String>

(keyed labels of UI elements), which is created dynamically via fetching the labels from api -- so not statically with string literals. Does it make sense to implement a

Trie

or is this somehow optimized under the hood in jvm since

String

is so special? I remember faintly about string interning, but that only applies to string literals and deals with copies, right? It might be more memory efficient, however what about lookup? I believe there are native implementations of this inside when simply matching

Strings

, no? Also, turning unicode strings to char arrays won't work all that great?

How do primitives work in kotlin?

public class Char private constructor() : Comparable<Char> {
    public fun toInt(): Int
    ...
}

First of all, what is this even, and why does it compile? a concrete class with no implementation of methods? Secondly, does

charArratOf('a', 'b', 'c')

create 3 instances of Char class? Or, is there some magic

Is this the correct behavior? Only is working inside functions

hi, Is it possible to print the names of my custom colors within a list?

Is there a way to have a data class secondary constructor provide a value for a non-primary-constructor

val

? 🧵 ->

Hi, If use a 3rd party library, like lets say moshi, and I create useful extensions, and useful columnadapters etc, and want to distribute this to other consumers (internally). How should I name this module? Is the X suffix common place in kotlin in user space as well?

:moshix

? or more conservative

:base-moshi

? (

:sqdelightx

,

:retrofitx

etc) same goes for my custom

Flow

operators, since flow likes to keep it bare bones

What’s the best way to ensure at least one of two class constructor params is non-null at compile time? For example in

data class Foo(val a: String? = null, val b String? = null)

I could write

data class Foo(val a: String? = null, val b String? = null)
{
  init {
         requireNotNull(a ?: b)
       }
}

But this only causes a crash at runtime. How do I achieve the same result with compile time safety?

I have an array of unsigned Integers (from 0 to 255)

val signerPrivateKey : IntArray = intArrayOf(6,199,39,185,82,199,26,124,50,54,50,128,200,204,220,164,48,77,49,31,9,228,77,61,123,53,62,86,163,183,9,172,101,133,107,31,215,181,167,87)

how do I convert it to a ByteArray?

I want to bring kotlin support to a java library without adding kotlin to it. What I want is to make a sealed class. Is there any kind of meta data or naming conventions I can use to make my classes work as a sealed class when consumed by kotlin?

Hello all, not sure if this is a noob question but here it goes: How can I get the difference between two List/ArrayList regardless of the order of the sentence? I mean, for example these two lists

val first = listOf(1, 2, 3, 4, 5)
 val second = listOf(1, 2, 3)

If I use

first.minus(second)

I’ll get

[4, 5]

but If I use

second.minus(first)

I’ll get

[]

Hi all! Question that has probably been answered before, but I couldn’t find/understand those answers: Why do we need to annotate “value classes” with @JvmInline? Ie. why is it not implied that a “value class” should be inlined? And what is a “value class” without @JvmInline?

Is there a stdlib function like

repeat()

but that returns the result as a collection? to the effect like

(0..i).map() { foo() }

?

Hello, Is there any kotlin library for Calendar that we want to use in CommonMain .......... like for java we use the same thing as 'Java.util.Calender'?

Are Jetbrains maintaining any Docker images? I'm looking for some easy and trusted way of getting access to

kotlinc

inside a Docker Image.

Why does the KMM application type generate an Android module with a "java" directory rather than a "kotlin" one? I suppose the more important (?) question is, is there any reason not to rename it "kotlin"?

Hi everyone, any recommendations for courses to learn kotlin from the start

Any good resource to read about comparator, comparables, sortedWith, compareBy? I want to sort objects based on multiple properties of object in custom ordering logic.

How do I order ids based on some logical ranking, let's say I have IDs of 1,2,3,4,5. But I want to rank them in order of 3,4,2,1,5. Here Id 3 is most important category and should be ranked first. Ids are Int

Imagine we have a websocket server that can send various message types (defined as strings). Now for each of these received messages we need to create instance of specific class. I was able to model this data using sealed interface and enum class:

sealed interface WebSocketMessage {
    data class Hello(data: String):WebSocketMessage
    data class Bye(data: String):WebSocketMessage
}

enum class WebSocketMessageType(val type: String, val kotlinClass: KClass<out WebSocketMessage>) {
    HELLO("hello", WebSocketMessage.Hello::class),
    BYE("bye", WebSocketMessage.Bye::class),
}

// get message
val webSocketMessageType = enumValues<WebSocketMessageType>().firstOrNull { it == type }
...

I wonder if there is a way to model this using one entity, so adding the new messages types require change in a single place 🤔

this is probably stupid, but I am not sure how to find an answer. in spring, there is a file defining:

fun MockMvc.get(urlTemplate: String, vararg vars: Any?, dsl: MockHttpServletRequestDsl.() -> Unit = {})

I defined my own version

fun MockMvc.get(urlTemplate: String, vararg vars: Any?, subject: Subject = WithMockUser.defaultUser, dsl: MockHttpServletRequestDsl.() -> Unit = {})

in a test, by mistake, I imported both extension function, but when doing

mockMvc.get("/uri")

the first one got called. I am curious, how is the order defined in this case? I thought it could be the order of imports, but I tried both combination and the result did not change:

import org.springframework.test.web.servlet.get
import my.own.get

or

import my.own.get
import org.springframework.test.web.servlet.get

made no difference

Is it possible to compose or extend annotations in kotlin? In java you could add an annotation as a property like

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SuperAnnotation {
    String value();
}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface SubAnnotation {
    SuperAnnotation superAnnotation();
    String subValue();
}

hello, i tried to google, but did not find anything. a want to make a real long fun name for my unit test, but met an error (screenshot) It happens only with a really long name of fun. Can i overcome it somehow?

Hi everyone, I tried to use 

<http://kotlin.io|kotlin.io>.path.createTempDirectory()

 to create temporary directory on my kotlinc 1.4.31 but failed on Windows, WSL2 and Mac. In the Kotlin playground web,  the code raises `SecurityException`(which is correct) but all my systems (including kotlinc and intelliJ IDEA) cannot resolve the package 

kotlin.io.path

 . Is there anything I need to do to use the 

kotlin.io.path

 package?

Question: How to check certain combinations of inputs in Kotlin I have a data class as below:

data class foo(
  val a: T?,
  val b: U?,
  val c: V?,
  val d: X?
)

This is sent as an arg to a function

bar(val foo: Foo)

Now in this function

bar

, I want to allow only certain combinations of foo's members e.g.

if(a!=null){
  // If a is input, nothing else is allowed
  if(b!=null || c!=null || d!= null) throw Exception()
}
if(b!=null){
  // If b is input, nothing else is allowed
  if(a!=null || c!=null || d!= null) throw Exception()
}
if(c!=null){
 // If c is input, d is allowed, a and b not allowed
   if(a!=null || b!=null ) throw Exception()
}

Obviously, more the args, the worse it gets. What is a cleaner way of doing this?

Writing a dsl, the getters aren't supposed to be used, so I'm writing this at the moment:

var maxGCPauseMillis: Int
            get() = error("invalid")
            set(value) ..

does anyone have a better solution?