and return@func?

what this

fun Int.foo(){}

?

not

fun foo(): Int {}

hi, i get an error while i am running request which the error is in this file at the query. they tell me

must not have replace block. For dynamic query parameters use @Query

.how do i fix this error?

what's an idiomatic way of saying "if null, run this and return null"? kind of like how

also

runs a function and then returns the original value, except that i only want to run the function if the original value is null i've got something like

value.takeIf { it >= 0 } ?: run { println("Warning: negative value"); null }

except i'd like to avoid manually having to return null at the end of the

run

I have a list of valid ids in a complex class (in my example a Pair). I have a separate list of ids. What's the best way of filtering the lists of ids to only contain ids that are present in the first case ? I'm using map to convert the list of pairs to a list of ids and then using contains in the example below. Is there a better way ?

@Test
    fun `test filter`() {

        val cars = listOf("1" to "Jag","2" to "Mini")

        val ids = listOf("1","2","3")

        val validIds = ids.filter { cars.map { it.first }.contains(it) }

        validIds `should equal` listOf("1","2")

    }

currently cleaning up a Java app so that I can convert it to Kotlin at some point. Which nullable annotation should I use? I'm on Java 11 and using Spring Boot so org.springframework.lang.NonNull would be available

is it possible to define an Interface that only allows data classes as implementations?

I'm a newcomer to Kotlin/JVM so I'm definitely doing something non-idiomatic ... I'm used to structural equality from functional languages and I've had a few bugs because my classes weren't data classes...

Cannot access class ’<class>’. Check your module classpath for missing or conflicting dependencies

What does this even mean exactly? I want to test code that depends on a certain library. But I cannot add that library to the test configuration, so I simply create some dummy classes with the same name & package name and mock them using mockk 🤔 Doesn’t seem to work though 😅

I would like to get a list of zoneddatetimes by hour between 2 zoneddatetimes

val startTime = Instant.ofEpochMilli(1589778000000).atZone(ZoneOffset.UTC) // May 18 @ 05:00 UTC
val endTime = Instant.ofEpochMilli(1589950800000).atZone(ZoneOffset.UTC) // May 20 @ 05:00 UTC

val res: List<ZonedDateTime> = startTime.hoursUntil(endTime)

//[May 19 05:00, May 19 06:00 ...]

So that I can do a group by day on it

val final = res.groupBy{it.day}.toMap()
{ May 18 -> 19 hours , May 19: 24 hours, May 20: 5 hours}

Is this possible?

How would I write unit tests for this?

CoroutineScope(Dispatchers.Main).launch {
    withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
        // do something here
    }
}

It always stops after withContext(Dispatchers.IO), im adding the TestCoroutineDispatcher @rule but it still does not work.

Hello guys, I have a problem when mocking a Kotlin class in Java with Mockito. The kotlin class has a

reified

method and my Mockito is presumably choosing the wrong method for some reason. So when running my tests, Mockito either chooses the method I want to mock or chooses the

reified

Kotlin method, which then turns into an Exception because the return types do not match. Did someone run into this problem already or know how to fix this?

cant we apply the spread operator on

List

?

is there a way to reference inline function in Java terms, I'm trying to create an ArchJUnit rule that specific function should not be used but how can I reference function without class name or fully qualified name

What's the general consensus on the best way to have a function that can fail in multiple different ways in Kotlin? I always thought we should use Result for that but just found out that it can't be the return type of a function. Should we just keep on throwing exceptions?

Is there an idiomatic way to “bridge” inlined reified functions to concrete named functions so that the inlined function is callable from Java? Such as the following two prototypes.

how do i construct a class where 1. the fields of the class can be set using named constructor arguments with default values 2. those fields are accessible and settable through a map without having to declare each variable twice (once as a field and once as an argument)? so far i've got the following not-quite-working example

class Test(
        first: String = "default",
        second: Int = 42,
        third: Boolean = false
) {
    val map = mutableMapOf<String, Any>()

    inner class MyDelegate(private val default: Any) {
        operator fun getValue(receiver: Test, property: KProperty<*>) =
                map.computeIfAbsent(property.name) { default }

        operator fun setValue(receiver: Test, property: KProperty<*>, value: Any) {
            map[property.name] = value
        }
    }

    var first by MyDelegate(first)
    var second by MyDelegate(second)
    var third by MyDelegate(third)
}

val t = Test(second = 100)
t.first = "test"
println(t.map) // {first=test} - WRONG
println("${t.first} ${t.second} ${t.third}") // test 100 false

but i don't like the redundant definitions (having to declare each field as an argument as well), and this example also behaves incorrectly in that the map doesn't get populated with all the arguments immediately upon instantiation

dsl patterns can lead to nested receivers, e.g.

project { all X@{ register {  
  foo(this@X)
}}}

is there a way for that inline receiver function to give the receiver an explicit name, other than

this

, instead of using the

@

label?

Hello! Is it considered bad practice to define extension functions for native types, such as

String

? Example, putting a function like this globally scoped in like a

StringUtils.kt

class:

fun String.getLinkIfPresent(): String? {
    val m: Matcher = urlPattern.matcher(this)
    if (m.find()) {
        return m.group().trim()
    }

    return null
}

running into some generics issues consider the following class hierarchy, consisting of a set of classes each with an associated "accessor". the idea is that e.g.

Child1

can be "accessed" using a

Child1Accessor<T>

object, which will return a value of type

T

.

abstract class Accessor<T>

abstract class Parent<A : Accessor<*>> {
    fun <T> access(accessor: Accessor<T>) : T = TODO("implement")
}


class Child1Accessor<T> : Accessor<T>()

class Child1 : Parent<Child1Accessor<*>>()


class Child2Accessor<T> : Accessor<T>()

class Child2 : Parent<Child2Accessor<*>>()


val myIntVal: Int = Child1().access(Child1Accessor<Int>())
val myStringVal: String = Child1().access(Child1Accessor<String>())
val error: Int = Child2().access(Child1Accessor<Int>()) // should be an error, wrong type of accessor

my issue is: how do i restrict the

accessor

parameter of

access

to be a subclass of

A

, the accessor type specified for that class, without using wildcard types, so that i know the type parameter of the accessor? i tried the following:

fun <T, V> access(accessor: V) : T
            where V : A,
                  V : Accessor<T> = TODO("implement")

but this gives me a

Type parameter cannot have any other bounds if it's bounded by another type parameter

error

Can someone help me get FreeMarker working with IntelliJ, please? 🙂 I'm doing the Ktor beginner app and she no worky.

I am migrating codebase from Rx1 to Rx2 and now that

null

is not supported by RxJava and RxKotlin, what is the strategy you use to have kind of null values? We have some places in codebase that were doing something like

map {
  service.get() //can return null
}.filterNotNull()

It's too much effort to rewrite every service to not ever return null when before null was considered a valid empty value.

Hello, how can I use a copy method like for data class with a non data class? I have a class that initialize a date = now() but I want to change it for a test case!

quick question, im trying to use the find method, but for some reason it returns

List<Test?>

and I want it to be just a List<Test>. how do I prevent the type of the elements in the list to be nullable? I want it to be an empty list worst case scenario

I have a function like this:

public final GoogleSignInOptions.Builder requestScopes(Scope var1, Scope... var2) { }

I can call

.requestScopes(scope1, scope2, scope3)

without any problem. How can I translate a list of Scopes to call this function. I tried using only an

Array

, a

List

, to pass the first element and then a list. But nothing worked. Seems like I have to pass the expanded list. How can I achieve this when my list of scopes is stored inside a

List<Scope>

? Thanks!

I'm trying to do something for a JSON parser. I have a bunch of properties named "%type%Sold" and "%type%Base" which contain a CountryCode and an amount. There's like 5 different times these repeat. I'm trying to figure out the best way to structure the model for this. I was trying to use sealed classes with data classes, but that seems rather unwieldy. Here's what I've got so far:

sealed class Amount(
  val currency: Currency,
  val value: Long,
  val type: String
) {
  data class Sold(override val currency: Currency, override val amount: Long): Amount(currency, amount, "Sold)

I don't quite understand the scope in Kotlin Gradle DSL. I understand that gradle build script implicitly import some stuffs. But for example in this code:

application{ mainClassName="SomeClass" }

where do the name mainClassName come from? I'm setting some attribute here. But where is the object? Shouldn't it be something like:

application.mainClassName="SomeClass"

Okay. I'm encountering, of all things, a potential critical bug with

kotlin.collections.ArrayList.indexOf

. I think it's critical, but maybe not. There are fixes but

indexOf

doesn't properly work for me in certain cases ( version 1.3.61) Premise:

val questionsAndAnswers = mutableListOf<Any>()

, in practice containing items of types data class Answer and data class Question. Both have

equals(other: Any)

overriden to return true only when other is of the same type. equals in Answer

override fun equals(other: Any?): Boolean {
            return (other as? Answer)?.proof?.sourceNode?.getContentId() == proof?.sourceNode?.getContentId()
}

equals in Question

override fun equals(other: Any?): Boolean {
            return (other as? Question)?.item?.getContentId() == item?.getContentId()
}

I do

questionsAndAnswers.indexOf(answer)

knowing my answers are only add odd indexes, and I get a 0. I expected either -1 or odd. Check the debugger, i mapped a bunch of data to help troubleshoot

I need to make an Observable with n number of items in it, but I don't know how to achieve this. Here's the code I'm using as an example:

device.establishConnection(false)
    .flatMap(rxBleConnection -> Observable.combineLatest(
        rxBleConnection.readCharacteristic(firstUUID),
        rxBleConnection.readCharacteristic(secondUUID),
        YourModelCombiningTwoValues::new
    ))
    .subscribe(model -> {
        // Process your model.
    });

Here's the code I am trying to write:

device.establishConnection(true)
    .flatMap { rxBleConnection ->
        val characteristicReads: MutableList<Single<ByteArray>> =
            mutableListOf()
        for (c in characteristics) {
            characteristicReads.add(rxBleConnection.readCharacteristic(c.uuid))
        }
        Observable.combineLatest(*characteristicReads)
    }
    .subscribe({ onConnectionSuccess(it) }, { onConnectionFailure(it) })

The error is:

Type mismatch.
   Required: ObservableSource<out TypeVariable(R)!>!
   Found: Unit