This is probably wrong -- but how can I fix it without using kotlin-reflect?

@ExperimentalStdlibApi
inline operator fun <reified T : Any> SharedPreferences.getValue(owner: Any?, property: KProperty<*>): T {
    return when (val type = typeOf<T>()) {
        is Set<*> ->
            getStringSet(property.name.replace('_', '.'), emptySet()) ?: emptySet()

        else -> error("Invalid type")
    } as T
}

If I have:

class Foo { fun get(): Something }

operator fun Bar.getValue(o: Any?, property: KProperty<*>): Something = Foo().get()

val prop by Bar()

Will the Foo instance get GCed?

What is an idiomatic way of calculating the power of two for integers?

I want to use HikariCP. I have a bunch of DAOs that implement an interface for CRUD operations. What is the best way to pass around the DB connection to get the best use out of connection pooling?

Im just here because one day I plan to work on some plugins, and I would rather use kotlin then java.

Hi Guys, i kind of hit a road block while doing practice questions in code wars 1. I have a doubleArray which contains distances

val x:DoubleArray = doubleArrayOf(0.0, 0.19, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.25)

the values are records every 1.5s distance travelled, in this case 0.0 is the starting point 0.19 is when the distance covered is recorded at 1.5 seconds mark after another 1.5 seconds the distance of 0.5 is recorded and so on. 2. I need to find the difference in distances as following

0.0-0.19, 0.19-0.5, 0.5-0.75, 0.75-1.0, 1.0-1.25, 1.25-1.50, 1.5-1.75, 1.75-2.0, 2.0-2.25

, i know how to use map(to double values or multiple then) but i don't know how to subtract from a preceded value with a previous value in an Array 3. you can refer to the full question if my explanation is not clear, i just need to find the difference in distances before i can proceed to do the next step, hope someone can help me on this 😅

I’m working with a java library that does something like this:

class Foo {
    public static Foo.Builder Builder() { ... }
    public static class Builder { 
        public Builder() { ... }
    }
}

and i’m trying to call it from kotlin like:

Foo.Builder()
...

but i get complaints about ambiguity…i think because the helper type in

Foo

matches the class name (and therefore the constructor) exactly. does anyone know if there’s a way to disambiguate between the two from kotlin?

How do I get the fields and types of a class similar to how kotlinx.serialization does it? (using kotlin native)

I am confused about secondary constructors. Kotlint avoid having an incomplete object constructed by forcing me to immediatly call the primary constructor. But I do not know how I can actually calculate the value for the primary constructor - I want to run code to calculate the value, that is the whole point of the second constructor. I can do it by using a function:

private data class MyClass(val intVal: Int) {
    constructor(stringVal: String) : this(someFunction(stringVal))
}

fun someFunction(stringVal: String): Int {
    println("I can run some random code here")
    val foo = stringVal.reversed()
    return foo.toInt()
}

But how could I run code on the secondary constructor without using a function?

I have a question regarding elvis operators. If I want to print something then return from a function if the value is null, how would I do that with an elvis operator? I tried to do this, but I get an error saying that return is not allowed here:

// getVal() returns a nullable value
fun example() {
    val myVal = getVal() ?: {
        println("value is null")
        return
    }
}

I had some hidden string formatting in one of my classes, and now that I want to write a test for it, I pulled it out into it's own class. It's your typical "Should I create a StringUtils class?" sort of question. Should I have

class StringUtil {
    fun getInitialsFromName(name: String): String {

or just create

class InitialGeneratorService {
    fun get(name: String): String {

Or should it be a companion or just make a string extension method (seems easily abused though) I'm definitely overthinking it, but approciate any advice

Lets say I have:

interface Foo
class Foo1 : Foo
interface Bar {
   fun <T : Foo> baz(foo: T)
}
// This doesn't work, why? It IS derived from Foo... is there any way to do such a thing w/o taking in a Foo and casting it to Foo1?
class Bar2 {
   override fun baz(foo: Foo1) = TODO()
}

Hello everyone, can someone help me with this coroutine problem please:

private suspend fun suspendFunction() : Boolean { ... }

launch {
    val returnedValue = suspendFunction()
    if (returnedValue) anotherFunction() // this does not fire in the debugger
}

What am I doing wrong?

Hi! I'm trying to use fragments for navigation.

findNavController(R.id.nav_host_fragment_content_main).navigate(R.id.settingsFragment)

I'm using this inside onOptionsItemSelected in the activity (I am trying to a settings fragment when I click on the button in ActionBar). Although this is working, if I click on the settings 5 times, I also need to click back 5 times. I am aware this is intended behaviour, but I can't seem to find how to avoid this.

Groovy allows

$

in identifiers (e.g.

A$B

is a valid identifier). Kotlin allows quoted identifiers like ``A$B`` . But https://kotlinlang.org/spec/syntax-and-grammar.html#identifiers states that letters are "<any unicode character of classes LL, LM, LO, LT, LU or NL>" and that identifiers are "(Letter |

'_'

) {Letter |

'_'

| UnicodeDigit} | `'`'` QuotedSymbol {QuotedSymbol} `'`'` ". Does that not mean that e.g. Ⅲ (aka \u2162) - which is part of unicode character class NL - should be a valid identifier? I just tried but the compiler does not like

val Ⅲ = "roman 3"

.

class Foo
class Bar

Why I can't do `Foo() == Bar()`but can

Foo().equals(Bar())

?

How would I go about implementing something like this:

fun <R> convertTo(): R {
    return convertImpl()
}

fun convertImpl(): Int {
    // ...
}

fun convertImpl(): String {
    // ...
}

Is there an easy way to do it or will I have to just use a when statement and make R reified and add a branch for each implemented type?

Hi, what is the better between

data class Zone(x: IntRange, y: IntRange, z: IntRange)

and

data class Zone(x1: Int, y1: Int, z1: Int, x2: Int, y2: Int, z2: Int)

? And would it impact performances to use Ranges ? I only need like 50 zones maximum for my project

Do we have compose-web channnel?

I have a simple app that makes a simple network request to get json. How do I convert that into an object without any 3rd party deps? I typically use gson or moshi for this sort of thing, but I don't think it's worth bringing in an entire library for this single network call. I know in java we used to just use some really bad Json apis, but I wonder if kotlin has anything else out of the box.

Hey, I'm getting started with kotlin and was wondering if there are any kotlin specific test assertion libraries like there is assertj for java? Builders seem like they would enable something interesting like

assert("asdf") {
  hasSize { it isEq 4 }
}

Hello, I have a function that uses generic that I would like to mock using mockito.

abstract class MyClass<T>(){
    abstract fun blocking(): T

fun <R> execute(run: (T)->R, onError: ((e: Throwable)->R)? = null): R {
        return runCatching { run(blocking()) }.getOrElse{ e -> onError?.let { it(e) } ?: throw e}
}
}

internal class MyClassImpl(): MyClass<String>() {
    override fun blocking(): String {
        return "something"
    }
}

I would like to mock the execute function in MyClassImpl that extends MyClass I usually mock functions as follows but it's not compiling as it can't infer the types

private val myVariable = mock<MyClassImpl>().also {
        whenever(it.execute(any(), anyOrNull()).thenReturn(any())
    }

Really appreciate the help.

Don't know where to ask this question, but am I allowed to show this Slack channel on my Twitch live stream?

Updated to Kotlin 1.6.10, but now I'm getting this build error. How do I solve this?:

java.lang.IllegalStateException: Symbol for kotlin.collections/mutableMapOf|-4813910536206556932[0] is unbound
	at org.jetbrains.kotlin.ir.symbols.impl.IrBindablePublicSymbolBase.getOwner(IrPublicSymbolBase.kt:52)

Trying to come up with a test function to assert that every member of a list is of a specified type. This what I’ve tried

fun assertListTypes(list: List<ParentType>, types: List<KType>) {
    assertEquals(list.size, types.size)
    types.forEachIndexed { idx, type ->
        assert(list[idx] is type)
    }
}

assertListTypes(list, listOf(typeOf<Class1>(), typeOf<Class2>()))

But the compiler didn’t like the

is

check on the KType. Any ideas?

Hello guys, we are pretty new on our team with Kotlin and we are trying to understand coroutines, we have donde two different examples and one works and the other doesnt, maybe you guys can shed some light onto why one works and the other doesn't? We have been breaking our heads down here and no luck so far. Here's the example 1, working:

Why is the compiler asking me for an

else

branch when I have covered all of the possible subclasses of

Foo

(sealed class) ? Was it always like this? I remember not having to implement an

else

branch before.

I want to create an extension function that is using the

apply{}

function inside. Like:

fun Foo.myFun() {
  bar.apply {
    this.doA()
    this.doB()
    this.doC()
  }
}

this

here refers to the type of

bar

, not to the type of

Foo

How can I use the instance of

Foo

inside the

bar.apply{}

?

I have a class with a

MutableList

as it's property. I want to iterate through this list and change values of elements. So I use

listIterator

and its

set

method to change element values. But when I exit a loop and print out a list from original object I see no changes. How do I change the original object?