Hi everyone! I have a strange behavior which i consider should not be happening, but any insight is welcome. Basically i have some interfaces: interface A, B, C. (Inherits from B and C) interface B (with some methods) interface C (with some methods) at some point in code i ask a class implementing interface A :

if ( class is B)

but it is returning false

Hi everyone, i am new and i started reading the language programming kotlin so i want to know how i can read Android with kotlin (the courses to read ...) Thanks for all 😃

Why I have “Unsafe use” here 🤔

👉 I am doing a poll regarding testing frameworks usage in Kotlin projects. I m curious what is community preference, so please drop your vote here: https://twitter.com/igorwojda/status/1361303356484898821

Is there a Flow interface to stdin?

Hey people, I have a “when” question. When faced with this a colleague of mine recommended a one line refactor but I can’t achieve it because.

fun fillFieldsForAttribute(attribute: Map<String, Any>): Any? {
    when (localVariable) {
        is TruParameter -> {
            localVariable.update(attribute)
        }
        is TruVoltage -> {
            localVariable.update(attribute)
        }
        is TruBatteryState -> {
            localVariable.update(attribute)
        }
    }
    return localVariable
}

The classes referenced after “is” are all a subclass of “TruAbstract” which contains “update” what I tried was

(localVariable as TruAbstract).update(attribute)
return localVariable

and this does not work Do you see any good idea for a refactor here?

Are there any plans for union types in Kotlin or at least KotlinJS? I heard mentions in one if the arrow meta talks that kotlin already supports union types, just doesn't expose them to public api. Curious to know why

feels like Spam ----vvv

intellij why does

getResource

give me null? I have a

.txt

file in the same directory with

MyClass.java

I print the class with this code

println(MyClass::class.java)

it returns me

class com.myapp.vendors.lib.MyClass

However when I want to get the txt file with this code:

println(MyClass::class.java.getResource("my.txt"))

it returns me null

This class can only be used with the compiler argument ‘-Xopt-in=kotlin.RequiresOptIn’

What is this warning for? I can use the class just fine even without that arguments 🤔 I guess the message is just misleading.

Hello everyone 👋 I'm trying to help a colleague of mine get access to this slack workspace, it seems the invite option has been disabled for me. Can someone please help point me in the right direction or offer some guidance on how they can get invited/access to this slack workspace?

what is the impact of setting

kotlinOptions.jvmTarget

to

JavaVersion.VERSION_1_8

or

JavaVersion.VERSION_15

– assuming i’m using Java 15? • (1.4.20 release notes where support for 15 was added) • (jvmTarget documentation) will my code run in an optimized manner – as it can take advantage of newer JDK features, etc?

I really miss union types. Or simpler error handling.

User | UserNotFound | NetworkError

instead of a dozen sealed classes all defining the same errors over and over again.

Still no 1.4.30 stable plugin for IDEA?

What is a better way than

val port = property.getProperty("notification.port").orEmpty().let { if (it.isNotBlank()) it else "7100"}

? Is there something like ``val port = firstContent(property.getProperty("notification.port"), "7100")` ?

Is it possible to make all items (classes/objects/interfaces/enums…) in the module

internal

by default?

It looks like Kotlin docs layout has been updated and now it's "impossible" to google "kotlin when expression" and find the right page. It only gives a spec page https://kotlinlang.org/spec/expressions.html.

I have 2 questions wrt sealed classes and `when`:

sealed class A {
    data class X(val m: Int) : A()
    data class Y(val m: Int) : A()
    data class Z(val m: Int) : A()
}
val x = when (val a: A = A.X(3)) {
    is A.X, is A.Y -> a.m  // <<<<<<<<<<
    is A.Z -> a.m
}

1. Why does Android Studio say

'when' expression must be exhaustive, add necessary 'else' branch

? Aren't all cases covered here? 2. Why is

a.m

no accessible on the marked line? It says

Unresolved reference: m

.

(Using the sealed class from the previous message) Is there a reason IDE doesn't suggest eliminating

when

altogether in this case?

val x: A = A.X(0)
when (x) {
    else -> 1
}

Maybe stupid question, but I m wondering one thing - is it smart to create a box for specialized array type in order to avoid having to override the

equals()

methods in each and every data class when I want to use one of these? 🤔 If so why such comparable variants of the spec. array types are not part of the STL yet? Obviously, I cannot use all the exension methods provided by the STL directly then.. but it still feels a bit better than messing up my domain model with all those overrides of equals() and hashCode() typically because of one single array field.. Something like this:

class ComparableByteArray (val array: ByteArray) {
    val size: Int
        get() = array.size

    constructor(size: Int) : this(ByteArray(size))
    constructor(other: ComparableByteArray) : this(other.array.copyOf())

    override fun equals(other: Any?): Boolean =
        (this === other) || (javaClass == other?.javaClass && array.contentEquals((other as ComparableByteArray).array))
    override fun hashCode(): Int = array.contentHashCode()
    override fun toString(): String = array.toString()
    operator fun get(index: Int) = array[index]
    operator fun set(index: Int, value: Byte) = array.set(index, value)
    operator fun iterator(): ByteIterator = array.iterator()
}

data class User {
   //....,
   secretKey: ComparableByteArray
   //...,

   // <-- Would have to override equals() and hashCode() here if I used just ByteArray so the data class loses its purpose
}

Why <*> generics are casted to Nothing by the compiler instead of Any?, e.g. why can't I implement such a function without unchecked casts?

fun <T: Any> T.toValuesSkipping(vararg skip: KProperty1<T, *>): Map<String, Any?> =
  (this::class.memberProperties - skip)
  .filter { it.javaField != null }.map { it.name to it.get(this) }.toMap()

ugh.... 😢 why this doesn't work

class Wrapper {
    sealed class Whatever {
        abstract val name: String
    }

    data class First(override val name: String, val first: String) : Whatever() // constructor is private....
}

Spent a whole day on the error "Class A cannot be cast to Class A" when trying to access

@Cacheable

method return value when it clearly should be working since I literally just put the same class instance into the cache when I called the method for the first time 1 second ago... Couldn't find a single article that helped me on the issue.

mvn clean

didn't help either. ... It worked after I invalidated intellij cache and restarted IDE. I love my life sometimes.

I'm looking for some wisdom on writing Kotlin libraries, specifically for Android in my case, specifically for helping write the couple of apps that I support. Sometimes I feel like it's too hard to balance what goes in the library and what goes in the app, or the libraries are too small and not worth it. Any tips?

Hi all, I’ve got quite some pieces of code in my application like this:

val product: Product = products.find { it.name = input } ?: throw IllegalArgumentException("Product $input not found")

I know that it will be very unlikely to not find the product in this list (say, impossible), so, I’d rather not clutter my code with the “if null throw exception” stuff, and rather have

find

throw an exception if the product can’t be found, like this:

val product: Product = products.find { it.name = input }

I’d rather not make Product nullable (

Product?

), cause that will lead to some if/then elses later in my code. Is there any clean way I’ve missed to accomplish this?

I'm trying to run a .class file compiled through Gradle, just for the sake of it but I haven't had any success. I want to use

java

, how can I make it run? I've tried stuff like this:

$ java -cp "/usr/share/kotlin/lib/kotlin-stdlib.jar:." kott.AppKt     
Error: Could not find or load main class kott.AppKt
Caused by: java.lang.ClassNotFoundException: kott.AppKt

$ java AppKt 
Error: Could not find or load main class AppKt
Caused by: java.lang.NoClassDefFoundError: kott/AppKt (wrong name: AppKt)

This message was deleted.

It very much depends on your software development and runtime constraints. What factors are important or critical for you?

Hi there, I am developing a binary serialization with kotlinx.serialization framework. I am currently stuck with serializing public keys (likely because it is an interface). The issue is that I can always serialize a public key, but to deserialize I need to know what kind of key this is. I did achieve such functionality using surrogates (as in docs) in simple cases such as

class User(val id: PublicKey)

but it does fail with generics

class<T> User(val id: T)

. I get

Class 'RSAPublicKeyImpl' is not registered for polymorphic serialization in the scope of 'PublicKey'.

when I insert a public key instance there. My minimally working example is here https://github.com/vnermolaev/serde Does anyone have experience with kotlinx.serialization and applying it together with generics?