aob = ByteArray(1024)

Hi everyone! I am new to kotlin and I am searching a way to use kotlin multiplatform for sharing codebase specifically between android and web platforms. could anyone help here by giving me any suggestion or resources that may be helpful.

What is the best pattern for where to implement equals/hashCode/toString in a class hierarchy where there is one interface with many implementing classes? I would like to define this in one place (because in this case the implementations would be the same for all classes). Kotlin doesn’t allow to define them on the interface. The obvious solution is have a single base class that all other classes extend from, but then that base class cannot be private (because other implementing classes are public) and what if a class is already extending a class.

Hey guys, how do I get the view of a fragment from my activity?

A question regarding

any

and `all`: do they short-circuit, or do they evaluate the predicates for the whole items?

Hey there! Could someone point me to some docs explaining why

val (_) = Unpackable("Two")

does not call

component1

?

In a companion object, is it acceptable practice for

operator fun invoke(...): MyClass?

to return a nullable value, or is that confusing to the caller since it looks like a constructor call?

Is there a standard library function to convert a sequence of sequences like this:

{{A}, {B, C}, {D, E}}

to

{{A, B, D}, {A, C, D}, {A, B, E}, {A, C, E}}

?

I haven't used Intellij for a long time so this is a new configuration. I am setting up my Java and Gradle for the first time on this system, for this Ktor quickstart project.

What is the

hashCode()

and

toString()

implementation for the cases where I don’t define a class as data class? For example when I examined with a class like this:

class ListNode(var elem: Int) {
    var next: ListNode? = null
}

fun main() {
    val node = ListNode(123)
    println(node.hashCode())  // 895328852
    println(node.toString())  // ListNode@355da254

    node.elem = 456
    println(node.hashCode())  // 895328852
    println(node.toString())  // ListNode@355da254
}

whereas when I examined when changing to data class:

data class ListNode(var elem: Int) {
    var next: ListNode? = null
}

fun main() {
    val node = ListNode(123)
    println(node.hashCode())  // 123
    println(node.toString())  // ListNode(elem=123)

    node.elem = 456
    println(node.hashCode())  // 456
    println(node.toString())  // ListNode(elem=456)
}

From this my assumption is that the

hashCode()

and

toString()

depends on the memory address when the class is not a data class, whereas in case of data class, it will not depend on the memory address but the properties which are defined in the primary constructor (which makes sense, since that would be what data classes are for and how they should behave). Is my assumption correct? And where can I see these default implementations for

hashCode()

, both for class and data class? I wasn’t able to find them.

This message was deleted.

I guess a "getting started" question although just shipped production full kotlin 😆 Will this be only evaluated once because

val

-ness, a sort of

lazy by

? Confused of the heuristics here. Should I make it

var

if I plan on it changing?

adapter

doesn't change, the

onActionPerformed

can

val onActionPerformed: ((String, Any) -> Unit)?
        get() {
            return adapter?.onActionPerformed
        }

Are these two equivalent (just checking for any gotchas)?

if (text.length < 40) {
    // left pad with zeros
    text = String(CharArray(40 - text.length)).replace('\u0000', '0') + text
}

text = text.padStart(40, '0')

not sure how to make the list-to-be-added iterable so that it can be fed straight into addAll

First time on Kotlin and intellij. Can anyone tell me why some of my function names in intellij have a strikethrough them? Here the

init

name has a strikethrough

will this replace the item found in

it.items

with a new object whose

toggled

variable is now changed?

it.items.map { item ->
    item.copy(toggled = createSearchParams?.condition?.contains(item.itemValue)!!)
}

i want to find an object inside items whose

item.itemValue

is equal to createSearchParams?.condition? and set the toggled status of that item to true

You might want this if you want to mutate the original list.

.map()

creates a copy of the original list

why not the string after

?:

?

i’m a big fan of never using lateinit

Is there a better way to achieve this:

enum class Boo(private val fooDelegate: String? = null) {
    BAZ,
    BAM(fooDelegate = "bar");

    val foo: String
        get() = fooDelegate ?: error("no foo set for ${javaClass.simpleName}.${name}")
}

I want that if

foo

is needed, it must have been set, but if it is not used, it is not necessary to set it. Optimally I like to access it by name

foo

and also set it by name

foo

instead of setting it by name

fooDelegate

or

optionalFoo

. When getting

foo

, I want it to be of type

String

though, not

String?

.

Is there a way to make a "javadoc" out of kotlin code?

How would I do this in IntelliJ? Is this possible?

Given these few lines:

open class A
interface B
class AB: A(), B
class CD: A(), B
fun <T> foo(t: T): Nothing? where T : A, T : B = null
val a = foo(AB())
val b = listOf(AB()).map(::foo)
val c = listOf(AB(), CD()).map(::foo)

The last one with

c

is not compiling. Does anyone have an idea how to make the last line also work? It gives the compilation error

Type parameter bound for T in fun <T : A> foo(t: T): Nothing? where T : B is not satisfied: inferred type Any is not a subtype of A

So it seems while the created list could be of needed types

A

and

B

, the type inference is not smart enough here but creates a

List<Any>

Is there a way to fix this, e. g. to explicitly define the List type somehow? Interestingly the type inference in IntelliJ is smart enough to handle it properly and does not show an error, only the compiler bails out.

Could somebody ELI5 the difference between KMP and Native?

I find myself wishing for a

union

type - I know it's not coming. Can anyone think of a less verbose way of implementing these combination of sealed classes?

val modifiers: MutableMap<String,Attribute> = mutableMapOf()
sealed class Attribute {
	data class fValue(val value: Float) : Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class iValue(val value: Int): Attribute()	{
		override fun toString(): String {
			return value.toString()
		}
	}
	data class sValue(val value: String): Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class bValue(val value: Boolean): Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class lValue(val value: Long) : Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
}

if it’s null i want to return addSearch(carsListingParameters) without the map, hmmm but those are two different datatypes then ..

I'm extremely new to Kotlin and usually code using Java. I'm using a few resources and they refer to a type of function called a top-level function. Does this mean instead of Util classes in Kotlin you would have top-level utility functions?

Hello at all. I've got some java objects that I'd need to convert to kotlin. Is there an idiomatic way of specifying constraints on data classes. Like the following Java:

public class TotallyMadeUpClass{
    private String username
    public String getUsername(){ return this.username }
    public void setUsername(String username) {
        if (username.length > 10)
        throw new IllegalArgumentException()
        this.username = username}
}