I Am trying to write UI testing in one of my compose project, can some one suggest best library to write this, previously we use robolectric

Can anyone tell me what is wrong with this?

I get date as string from backend and now at first I need to convert it to date time and then to compare this date and current date difference in years, months, weeks, days, minutes and seconds. In JS I can do this easily with moment JS like this

function extractTime(time) {
  return {
    seconds: moment().diff(time, 'seconds'),
    minutes: moment().diff(time, 'minutes'),
    hours: moment().diff(time, 'hours'),
    days: moment().diff(time, 'days'),
    weeks: moment().diff(time, 'weeks'),
    months: moment().diff(time, 'months'),
    years: moment().diff(time, 'years'),
  };
}

Is there something similar in Kotlin that I can achieve same result?

Is this how you return an empty lambda from an

if ... else

expression?

val myLambda: () -> Unit = if (condition) doSomethingLambda else {{}}

I have a tree represented by a Map<String, String> mapping child node it to parent node id. I now want to compute all the paths for this tree, starting at given node of the tree. Right now I have the following code, but I have the nagging feeling that I'm missing some more functional approach for this:

val tree = mapOf(2 to 1, 3 to 2, 4 to 3, 5 to 1)

fun allPath(tree: Map<Int, Int>, root: Int): Map<Int, List<Int>> {
    return (tree.keys.associateWith { path(it, tree, root) } + mapOf(root to listOf(root))).filterValues { it.isNotEmpty() }
}

fun path(start: Int, tree: Map<Int, Int>, root: Int): List<Int> {
    return buildList {
        var n: Int? = start
        while (n != null && n != root) { add(n); n = tree[n] }
        if (n == null) return emptyList()
        add(root)
    }.reversed()
}

println(allPath(tree, 1)) // prints {2=[1, 2], 3=[1, 2, 3], 4=[1, 2, 3, 4], 5=[1, 5], 1=[1]}

Am I using sealed classes correctly in this scenario?

sealed interface UserType {
  object GUEST : UserType
  class AUTHENTICATED(
    val authToken: String,
  ) : UserType
}

Would be happy if someone can help

I have found myself writing some snippets similar to this. Is there a better way to do it?

fun updateUser(username: String? = null, email: String? = null, token: String? = null) {
  if (username != null) {
    _appUser.value = _appUser.value?.copy(username = username)
  }
  if (email != null) {
    _appUser.value = _appUser.value?.copy(email = email)
  }
  if (token != null) {
    _appUser.value = _appUser.value?.copy(authToken = token)
  }
}

I have a base class and two child classes extending this parent class. Can I declare a return type of the method in the parent class so that it will return the type of the child class that is extending it?

open class Parent {
  fun load() {
    return ... // don't know what to return here
  }
}

class ChildA : Parent () {
  fun methodA() = ...
}

class ChildB : Parent () {
  fun methodB() = ...
}

class Usage {
  fun fooA() {
    ChildA().load().methodA() // I want to achieve this chaining
  }

  fun fooA() {
    ChildB().load().methodB()
  }
}

Is there a better way to do function calls similar to this?

someFunction(  // takes varargs
    *arrayOf(if (condition) "someValue" else null).filterNotNull().toTypedArray(),
)

For "reasons" we have in our Gradle build logic

import org.gradle.api.Action

inline fun <T> action(crossinline block: T.() -> Unit): Action<T> {
   return object : Action<T> {
      override fun execute(t: T) {
         t.run(block)
      }
   }
}

But updating Gradle to 7.5 and thus Kotlin to 1.6.10 now gives a compilation error (well warning, but we have

-Werror

) about wrong nullability:

w: ...\buildSrc\src\main\kotlin\...\util\SamHelper.kt: (10, 7): Override 'fun execute(t: T): Unit' has incorrect nullability in its signature comparing with overridden 'fun execute(p0: T): Unit'

What is his problem suddenly and how do I mitigate it?

I have this data class in Stat, all properties have some default value.

data class Stat(
    val bR: Int?  = 1,
    val cS: Int? = 2,
    val fP: Int? = 3,
    val gA: Int? = 4,
    val gC: Int? = 5,
    val gOB: Int? = 6,
    val gS: Int? = 7
)

How do I get all properties and their respective values of an object? val stat = Stat( ) stat.forEach { property, value } Is this possible in Kotlin?

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Which of these is likely to perform better? I assume the

List

version but you never know, figured I'd ask others:

fun recur(...): Sequence<*> = sequence {
    yield(...)
    getQueryRelations(innerRequest).forEach {
        yieldAll(
            recur(...)
        )
    }
}

fun recur(...): List<*> {
    return listOf(...) + getQueryRelations(innerRequest).flatMap {
        recur(...)
    }
}

I'm writing a DSL. It's something like this.

class Scope {
    fun method(block: () -> Unit) {}
}

fun scope(block: Scope.() -> Unit) {}

fun main() {
    scope {
        method {
            method {  } // I want to disallow using the scope inside the method
        }
    }
}

I want to disallow calling method on the

Scope

inside the

method

. I know I can have a dummy receive object and mark the

Scope

and the dummy object

DslMarker

.

@DslMarker
annotation class MyDslMarker

@MyDslMarker
class Scope {
    fun method(block: Context.() -> Unit) {}
}

@MyDslMarker
object Context // Dummy object

fun scope(block: Scope.() -> Unit) {}

fun main() {
    scope {
        method {
            method {  } // Compiler error now
        }
    }
}

Any better solution?

Hi, this piece of code works fine but it looks odd to me (all the exclamation marks!)... I suspect I am not making the best use of the Kotlin language. Could you please give me your opinion? If it can be done better, what would I need to work on?

val skillRating = MutableLiveData(0)
    fun calculateSkillRating() {
        if (readWinCount.value != 0 && readLossCount.value != 0) {
            skillRating.value = averageWinningScore.value?.plus(
                (400 * (readWinCount.value?.minus(readLossCount.value!!)!!) /
                        (readWinCount.value?.plus(readLossCount.value!!)!!))
            )
        }
    }

is there a difference between anonymous function

val a = fun (): String {
   return ""
}
or 
val a = fun () = ""

and lambda expression

val b: () -> String = {
   ""
}
or
val b = { "" }

in any way other than just the syntax?

Can anyone shed some light as to why the compiler is raising an “Overload resolution ambiguity” in the following?

fun CtxA.action() = CtxA
fun CtxC.action() = Unit

context(CtxA, CtxB)
fun bothContexts() {
    // Overload resolution ambiguity. All these functions match.
    // public fun CtxA.action(): CtxA defined in root package in file CtxRcv.kt
    // public fun CtxC.action(): Unit defined in root package in file CtxRcv.kt
    action()
}

context(CtxA)
fun onlyCtxA() = action() // works fine

As far as I can tell, it shouldn’t even be considering

CtxC.action

as a candidate as it’s not in scope. I can qualify as

this@CtxA.action()

but obviously not ideal.

Is there a way to change parameter names of extension functions? Say we have:

fun SomeClass.someFunction(param: Int) {
    // Do something...
}

We would invoke it as

SomeClass().someFunction(5)

and in Java it would be

KotlinClassKt.someFunction( /** this$SomeClass **/ SomeClass(), 5)

So my question is, can I change the parameter of the function?

Hi, is there a First In First Out collection in Kotlin which we can set a limited size ?

Meta question, does anyone know how to get invited to the JB Fleet discord?

I've been writing a relational DB in Kotlin as a learning exercise, and I'd like to implement codegen for the expression evaluator (it's currently interpreted) In Scala you have

quasiquotes

, which let you quote Scala code to have it be evaluated as an AST + compiled instead of interpreted This makes codegen really easy compared to using something like Janino Does Kotlin have something similar? Maybe in the K2 internal API's or something? I didn't find anything on Google searching for

kotlin codegen library

=/

Essentially I want to implement the equivalent of this:

def eval(e: Expression): AST = e match {
  case Literal(value) => q"$value"
  case Attribute(name) => q"row.get($name)"
  case Add(left, right) => q"${eval(left)} + ${eval(right)}"
}

Is there a way to mark an interface method, so the IDE would show a warning when calling it, unless suppressed?

Hello all - Any good suggestions on who to follow in the Kotlin community?

Hi! Can someone tell me what is

jvm-abi-gen

compiler plugin that was mentioned in 1.7.20-Beta release notes? I can not find any documentation on it.

Is there a way to create objects array without filling and manually fill it afterwards? Like, in my case I have something like this, but it's a bit ugly, and it does unnecessary filling array with

null

val tempLines = Array<IntArray?>(width + height) { null } as Array<IntArray>
            for (x in 0 until width) {
                tempLines[x] = IntArray(height) { y -> x + y * width }
            }
            for (y in 0 until height) {
                tempLines[y + width] = IntArray(width) { x -> x + y * width }
            }

Creating two arrays and concatenating them via

+

is not an option, because performance is very critical

Hello Anyone can help me how to save MP3 file in android/data/package name/files directory