Given a data class like this:

data class State (
	val aField : String
	val bField : String
	val cField : String
)

I would like to wrap this copy function:

wrapperobject.state = wrapperobject.state.copy (aField = aValue, bField = bValue)

inside a custom method like this:

wrapperobject.changeState(aField = aValue, bField = bValue)

what would be the code for it? I am not sure how to define the argument of the

changeState

method

Is there any reason why something like

isNotNullOrEmpty

doesn't exist by default? I hate having to do

!something.isNullOrEmpty

Both

when (it) {
    is EventDriver.Stop -> ...
    is EventDriver.Go -> ...
}

and

when (it) {
    EventDriver.Stop -> ...
    EventDriver.Go -> ...
}

seem to compile and run fine. What's the difference? I would have expected

is

to be required here?

Hey, I’m just wondering if there are any interesting use-cases of suspend functions outside of the two obvious ones: coroutines and generators?

Hello Kotlin Community. I'm looking for a deep dive in Kotlin with Spring Boot. I'm new to Spring and don't have any Java Experience. This is why most ( actually good) Tutorials don't bring me further. Thanks for your help 😘

is it possible in kotlin to retrieve a value previously calculated for sorting, so that I don’t have to calculate it twice?

myList
.sortedBy { val calculatedField = it.fieldA / it.fieldB }
.mapIndexed { index, elem -> MyNewObject(
    _index = index+2, 
    _value = calculatedField,
    _fieldA = fieldA.toInt()
    _fieldB= fieldB.toInt()
  )
}

unfortunately this code doesn’t work: I can’t access calculatedField from inside the map function

Is

==

and

equals

same in Kotlin? If so, can someone help me why my program is returning

false

for below inputs

John 19 0
John 19 22

import java.util.*

data class Client(val name: String, val age: Int, val balance: Int) {
    fun equals(other: Client?): Boolean {
        return this.age == other?.age && this.name == other.name
    }
}

fun main(args: Array<String>) {
    val input = Scanner(System.`in`)

    val n = input.next()
    val a = input.nextInt()
    val b = input.nextInt()

    val nn = input.next()
    val aa = input.nextInt()
    val bb = input.nextInt()

    println(Client(n, a, b) == (Client(nn, aa, bb)))
}

I would like to write a test method to check whether every field of an object is not null. So if I have a data class

data class Test(val property1: String?, property2: Int?)

and I would like to check if that property1 and property2 are not null. But I would like this generic for any object, not this specific one. I currently check, if the String of the object does not contain null, BUT this feels a bit hacky. Any idea how I can do that better?

I have a java method written as such

static Function1<MyManager, String> doTheManaging(){
    return MyManager::condense;
}

The kotlin converter can't seem to convert this. Can anyone point me in the right direction? Converter gives me a new companion object then

fun doTheManaging(): Function1<MyManager, String> {
 return { valueMap: Map<String, Any> -> condense(valueMap)}
}

but the entire return statement is red

After updating to Kotlin 1.4, I get a couple of type inference issues regarding

emptyList()

for example:

val retrievedList = myMap[someKey] ?: emptyList()

now gives a compiler warning (though the IDE doesn’t complain) when trying to access items in

retrievedList

so I need to explicitly set

List<MyListItemType>

as the

retrievedList

type or the

emptyList()

generic. I can’t seem to reproduce this in the kotlin playground, so can only assume there is some inconsistency caused by my gradle build scripts or some build caching issue.

Hi guys What article about kotlin coroutines you would recommend must read? I am trying to wrap my head around of how coroutines works in nutshell. Thanks in advance

Does anyone know why this happens? I started a fresh gradle project with Kotlin for JVM, it appears all grey

is this the best we can do ?

pages.toMutableMap().apply { this[currentPage] = it }.toMap())

Is it possible to split inner classes to separate files somehow?

Im sure everyone else knows this, but i havent been able to google/ stackoverflow this: in

scope.launch{}

, what do you call those curly braces? I know the last parameter type seems to have to be a lambda, often called

block

Is there a way to see if a device is capable of making telephone calls? Either to cell or landline? I know, in theory, someone with Skype installed could make calls through that, but I just want to check the main phone capabilities, and then hide a list of contact buttons should the device not be capable of making calls

Hi all, this is probably a newbie question. but i'm curious to know, whether in kotlin you can call components from other file into main file. i've tried to research about this before, but i can't find any resources that explaining about this stuff. here is the example of what i mean: main.xml

<LinearLayout
   android:id="@+id/linear_main"
   xmlns:android="<http://schemas.android.com/apk/res/android>"
   xmlns:tools="<http://schemas.android.com/tools>"
   xmlns:app="<http://schemas.android.com/apk/res-auto>"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="horizontal"
   >

   <TextView
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:text="Hello World"
			android:textColor="@color/Black01"
			/>

  /*insert some kind of tag in here to call the id of new_image element from second_file.xml*/


</LinearLayout>

second_file.xml

<LinearLayout
   android:id="@+id/linear_second"
   xmlns:android="<http://schemas.android.com/apk/res/android>"
   xmlns:tools="<http://schemas.android.com/tools>"
   xmlns:app="<http://schemas.android.com/apk/res-auto>"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="horizontal"
   >

   <ImageView
            android:id="@+id/new_image"
			android:layout_width="wrap_content"
			android:layout_height="wrap_content"
            app:srcCompat="@drawable/button_image"
			/>

</LinearLayout>

Hi all, tried to find an answer on Google/SO but not had much luck - I want to create a class that extends Constraint Layout so that I can add it dynamically to a view based on a toggle switch. I know that extending ConstraintLayout requires 3 constructor methods, but is there a way to pass in additional parameters when initializing the cutsom class? Ie. an array that I can then use in the custom class?

Has anyone else here been running into long start up times for unit tests that use mockks? It takes 2-3 seconds compared to a unit test without mocks running in ~250ms. I’m on Kotlin 1.4.0 and Intellij 2020.2 with a JUnit 5 unit test. The goal is to have all unit tests running around ~300ms if possible. The mockk unit test is below:

import io.mockk.every
import io.mockk.mockk


import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test

class ViewControllerTest {

    private val repository: TaskRepository = mockk()
    private lateinit var viewController : ViewController

    @BeforeEach
    fun setUp() {
        viewController = ViewController(repository)
        every { repository.findTasksFromView(any()) } returns emptyList()
    }

    @Test
    fun getView() {
        val list = viewController.getView(1)
        println(list)
    }
}

The regular unit test is here:

import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.assertAll
import kotlin.test.assertEquals

internal class TaskTest {

    private val project: Project = Project(1, "Inbox","The default project", emptyList())

    @BeforeEach
    fun setUp() {
    }

    @Test
    fun `maps Task to Viewable using extension function`() {
        val task : Task = buildTask()
        val viewable : Viewable = task.toViewable()
        assertViewable(viewable)
    }

    private fun buildTask() : Task {
        return Task(
                1,
                "Get focused",
                "TODO",
                project
        )
    }

    private fun assertViewable(viewable: Viewable) {
        assertAll(
                {assertEquals(1, viewable.id)},
                {assertEquals("Get focused", viewable.name)},
                {assertEquals("TODO", viewable.status)},
                {assertEquals(project, viewable.project)},
        )
    }
}

Someone else is having the same issue on StackOverflow: https://stackoverflow.com/questions/62208145/why-is-mocking-so-slow-to-start-in-kotlin

this seems weird to me - i have a kotlin class that implements an interface by a delegate (using the

by

keyword). the interface is defined in java and has some 

default

 methods. my class does not override those methods. i was expecting them to be forwarded to the delegate, but instead the default version is used. do i have to explicitly override all

default

methods in order to forward them to the delegate?

Hi! What is the correct matcher for a parameter Supplier<T>?

Hello! Is there method like in JavaScript match() which returns list by regex?

Hello. just started learning Kotlin for a new android project. This is a great starter application https://github.com/mrcsxsiq/Kotlin-Pokedex and i've got IntelliJ running with a korge multiplayer plugin. Wonder if any veterans had any advice for learning materials, IDE extensions or start-projects?

Is it possible to verify(mockk) a service that gets called which is inside a class inside a method of the class being tested?

how can I turn this back into a list after doing the operation in its lambda to each of the items in the list?

Hi all Why do I need parentheses at the end of the following inheritance:

class NoInterestsFound : RuntimeException()

It is common the define a data class like this:

data class Connector(val url: String, val username: String, val pw: String) {

    fun connect(): Database = Database.connect(url, "com.impossibl.postgres.jdbc.PGDriver", username, pw)

}

why would object (of a data class)

.toString()

not print its contents and only print the type?

Hi all - I’m trying to use SharedPreferences in my app in order to save a few preferences that then need to update pretty instantaneously inside the app. I have a settings page, where the user can switch from light to dark mode, and also update the voice of a TTS functionality. When the user ‘saves changes’ - I call editor.putXXXX(key, value).apply() for each setting and then close out of the settings page. Unfortuntately, I neither see the settings changed in my main activity, nor see the updated settings when I go back into the settings page. I understand that .apply() is asynchronous - I suspect that calling .apply() for each setting is going to cancel previous calls to .apply() - am I able to make several “puts” and then call .apply() just the once to make those several changes in one go? Why would I not see immediate changes in my main activity even if I call ‘sharedPrefs.getXXX’ again? I’m assuming it’s just an issue whereby the apply() function hasn’t actually finished yet? I’ve tried Googling and SOing for solutions but not getting anywhere