Hey guys, I want to build a RESTful API with Kotlin. What is the best Framework for that?

What’s the preferred style to fallback to a default value when accessing a map?

map[key] ?: defaultValue

or

map.getOrDefault(key, defaultValue)

?

val stepsize = piv.size() / Runtime.getRuntime().availableProcessors()
                (0 until piv.size() ) .step(  stepsize).map {
                    it until minOf(piv.size(),it+stepsize)                       
                }

is there an easier way of getting chunked IntRange sequences ?

Not sure if

gson

lib question is correct here. Anyway. My problem: I'm parsing diverse JSON objects which come wrapped in a generic JSON structure. I have a function where I've to "unwrap" the nested objects, i.e. extract them from the generic structure and parse the nested object with a generic type

T

.

trying to wrap my head around Contracts.

class Person(val email: String?)
inline class Email(val value: String) 

fun Person.email() {
  return this.email?.let {
    Email(email)
  } 
}

basically an extension method on a class that will null-check a value and return it wrapped in an inline class. how do i tell the compiler that if the function

Person.email()

returns non-null then the

instance.email

property is also not null. is that possible? am i fundamentally misunderstanding contracts?

I have a library with a few dependencies, org.json for example. If I want to use this in other projects without specifying the dependencies there was well it looks like I need to create a "fat jar" that packages up everything. I did that via gradle using the line below but now it includes everything such as the kotlin stdlib which seems a bit unnecessary, is that required or a way to exclude it? I can see how it might be needed if you used this library in a pure java project or maybe its just best practice to have it all for version conflict issues, not sure what is best practice here. jar { from { configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) } }}

Hi, is there a way how to hide (at least for autocomplete) a kt function in java ?

shouldnt it be bad practice to do validation inside the constructor of a data class, when u can just use the copy method to create another “valid” object ? My best idea to solve it so far is to wrap a data class inside a normal class, to avoid the copy method, but still have the benefit of data classes

Is it possible to use generic type on a high order function? Like this? I need the type of the "function" to be inferred.

help, any ideas how to implement this?

Hi All, how is overriding properties with a backing field handled? Does the overridden property reuse the backing field of it's parent class? Or does it shadow it?

Hi all, We were trying to bump Kotlin to 1.3.61 but ran into an issue where we cannot test

internal

anymore from the

test

folder of the module. Is this not allowed anymore?

Hi! Started working with kotlin in prod but still not sure if i'm doing that right/performatc way. Suppose I have a User collection and a Pair<UserId,Tag> collection, Each User object has a String collection property where I have to associate the given Tags owned by this user. In other words, a typical OneToMany join. Would this be the best way? How could I use parallelism in the outer loop (since the operations wont mix up cause every tag has its own user)?

val users = getUsers().apply {
        val tags = <get list of Pair<userid, tag>>

        forEach { user ->
            user.tags.addAll(tags.filter { it.first == user.id }.map { it.second })
        }
    }

Hey guys, just curious. What this arrow symbolizes? Where I can read about it? I couldn’t find it on Google I am running Kotlin 1.3.50 with Coroutines

For

typealias

naming - which style do you prefer?

() -> Int

// 1
typealias ProvideNumber = () -> Int

// 2
typealias NumberProvider = () -> Int

Usage then becomes either

provideNumber()

or `numberProvider()`/`numberProvider.invoke()`

I have

val items: Set<Any>

that contains different types including

EventItem

. I wanna find in my set the index of

EventItem

with the specific date like:

val event = state.items
    .filterIsInstance(EventItem::class.java)
    .find { it.start == date.atStartOfDay() }
                
val index = state.items.indexOf(event)

However, it gives me

Type inference failed. The value of the type parameter T should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.

What’s missing?

Hello, it is possible to use kotlinx-io in the multiplaftorm project? I have included

implementation "org.jetbrains.kotlinx:kotlinx-io-common:$kotlinx_io_version"

inside the commonMain block but gradle keeps saying it couldn't find such library

Could not find org.jetbrains.kotlinx:kotlinx-io-common:0.1.16.
     Searched in the following locations:
       - <https://jcenter.bintray.com/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://jcenter.bintray.com/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jar>
       - <https://dl.bintray.com/kotlin/ktor/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://dl.bintray.com/kotlin/ktor/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jar>
       - <https://repo.maven.apache.org/maven2/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://repo.maven.apache.org/maven2/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jarCould> not find org.jetbrains.kotlinx:kotlinx-io-common:0.1.16.
     Searched in the following locations:
       - <https://jcenter.bintray.com/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://jcenter.bintray.com/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jar>
       - <https://dl.bintray.com/kotlin/ktor/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://dl.bintray.com/kotlin/ktor/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jar>
       - <https://repo.maven.apache.org/maven2/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.pom>
       - <https://repo.maven.apache.org/maven2/org/jetbrains/kotlinx/kotlinx-io-common/0.1.16/kotlinx-io-common-0.1.16.jar>

According to ktor docs, it should work https://ktor.io/kotlinx/io/setup.html

Also, even worse, what about different kotlin versions also?

hello, does anyone know a way to display the difference between two list (of data class) ? either by debug in ide or to a string like apache diffbuilder difference = which item and which part of the item is different

Hi, is it possible to cast to two interfaces at the same time... without having "combining" interface Like cast some object to Comparable and CharArray at the same type, so function of shape fun <T> doStuff(param:T) where T : Comparable, T : CharArray can use the cast object?

Does anything really disasterous happen if you call

runBlocking

from a coroutine scope or does it just take over the thread while executing?

Is there an easy way to get a

KFunction1<T,R>

from a closure ?

Is there a better way to use the immutable builder pattern than this ?

fun LocalDate.set(year: Int?, month: Int?, day: Int?) : LocalDate {
    var tmp = this
    if (year != null){
        tmp = tmp.withYear(year)
    }
    if (month != null){
        tmp = tmp.withMonth(month)
    }
    if (day != null){
        tmp = tmp.withDayOfMonth(day)
    }
    return tmp
}

Is there an elegant way to map from and to string values of an enum, which has to be deserialized by gson?

enum class MyEnum {
    @SerializedName("my_foo") FOO // "my_foo" -> FOO (for deserialization)
    ...
}

MyEnum.FOO.string // FOO -> "my_foo"

hello together, a question concerning kotlintest. is it possible to organize tests via suite files like in junit or testng?

When using the

when

expression to test some cases, why do I have to use the

is

keyword sometimes, and other times I don’t?

is there any nice audio lib for kotlin?

would it be accurate to say that

if

is a top-level function with the following signature?

fun if(condition: Boolean, action: () -> Unit)

I tried to write a generic extension function for lists that returns all subsets of a given size that would be :

fun main() {
	val elements = listOf('A', 'B', 'C', 'D', 'E', 'F')
	val subsets = elements.getAllSubsets(3)
	subsets.forEach {
		println(it)
	}
}

desired output:

[A, B, C]
[A, B, D]
[A, B, E]
[A, C, D]
[A, C, E]
[A, D, E]
[B, C, D]
[B, C, E]
[B, D, E]
[C, D, E]

here's my implementation:

fun <T> List<T>.getAllSubsets(size: Int): List<List<T>> {
	fun <T> getAllSubsetsRecursive(
		elements: List<T>,
		currentSubset: MutableList<T>,
		remaining: Int,
		minimumIndex: Int,
		results: MutableList<List<T>>
	) {
		for (i in minimumIndex until elements.size - remaining) {
			val currentSubsetCopy = currentSubset.toMutableList()
			currentSubsetCopy.add(elements[i])
			if (remaining == 0) {
				results.add(currentSubsetCopy.toList())
				continue
			}
			getAllSubsetsRecursive(
				elements,
				currentSubsetCopy,
				remaining - 1,
				i + 1,
				results
			)
		}
	}

	val results = mutableListOf<List<T>>()

	getAllSubsetsRecursive(
		this,
		mutableListOf(),
		size - 1,
		0,
		results
	)

	return results.toList()
}

it does the job, however this still feels a bit verbose and messy to me, especially considering how often I create a copy of a list. is there any cleanup potential here?

For a map backed property, I’m able to return null. I’m wondering if this is normal/expected.

class MyClass {
    val map = mutableMapOf<String, Any?>().withDefault { null }
    var name: String by map
}

I cannot set

name

to

null

, but getting it returns

null

. This seems strange, given that the property has type

String

and not

String?

. Also, the IDE tells me the question mark in

name?.toString()

is unnecessary.