What is the meaning in this context?

It is possible to have Java and Kotlin in the same package right?

Is there by any chance an equivalent in Kotlin of .NET

Enumerable.Select

to convert from enumeration<type1> to enumeration<type2>? Thanks!

how do i create data objects in kotlin similarly to what i could do with javascript:

const myObject = {
  someKey: someValue,
  someOtherKey: [{foo: "bar"}, {bar: "foo"}]
}

is there any way to mark the class generated by

@file:JvmName("...")

as

@Deprecated

?

Hi all, I have the following code:

ProcessBuilder("/bin/sh", "-c",
      "java -jar $jarName -f $configName ${args.joinToString(" ")} &")
      .start()

how can I redirect stdout of the child to stdout of the parent process (so I could see all the messages together) ? The following code using

inheritIO

doesn't work either:

ProcessBuilder("/bin/sh", "-c",
        "java -jar $jarName -f $configName ${args.joinToString(" ")} &")
        .inheritIO()
        .start()

Any clue where the problem is ? Is it somehow related to the fact that the child process writes to log file ?

but when I do Foo..Foo its a type of ClosedRange<Foo> insead of FooRange that I've implemented

whats the best way to convert from a list of objects (think database results) to a nested object set. For instance a JDBC results set that used

GROUP BY day, status

which would give me a list with the same day more than once and the same status more than once which returned a list of

data class DayStatusCount(val day:LocalDate, val status:Status, val count:Long)

If I wanted to convert to a

Map<LocalDate, Map<Status, Long>>

or anythings similar to that. I've been creating mutable maps.

val rawData: MutableMap<LocalDate, Map<Status, Long> = HashMap()
        data.forEach {
            rawData
                    .getOrPut(it.day) { HashMap() }
                    .getOrPut(it.status) { HashMap() }
// More as per step
        }

Sorry thats not the real code. but anyway convert from a list with duplicates to nested sets.

How can I sort by a method that returns Boolean in Kotlin? I was using

Comparator

which returns an

Int

but now I need more complex stuff, so I have a method that returns

True

or

False

depending of a check, is there any way I'd use this method to sort it? Is getting

Foo1

Foo2

as a parameter and then do the comparation.

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We have an API endpoint that receives XML data from a 3rd party provider. The data itself is basically a list of elements, where each can be one of many different polymorphic types. They all share some attributes (say they all have a created_at="") and then some specific per element. Looked into using Jackson but it all seem very cumbersome, whats' the easiest way to parse this XML? An example could be

<?xml version="1.0" encoding="UTF-8">
<provider version="1.0">
  <update id="12313">
    <event name="hello" created_at="2019-12-14" />
    <event name="world" created_at="2019-12-16" />
    <country where="us" created_at="2019-15-16" />
  </update>
</provider>

Basically want to end up with a class containing

ProviderUpdate(id: String, updates: List<Update>)

where

Update

is either an interface, class, sealed class or something, that can either be

Event

or

Country

or etc

How do you deal with "flag" enums in Kotlin? Let's say I have flags 1,2,4,8 in my enum and from parsing some data, I obtain 5 (1 and 4 combined). How do I convert that 5 back into some enum value? In .NET, you have these "flag" enums and they are quite useful.

Why is

lateinit var

not allowed for inline classes that wrap types that otherwise can be

lateinit

-ed? For example:

inline class Id(val value: String)

can’t be used as

private lateinit var id: Id

and is there a workaround that is not a nullable field or a data class?

if I have the following:

inline fun defaultCheck(result: VkResult) = result.check()

fun bar(check: (VkResult) -> Unit = ::defaultCheck) {
   check(..)
}

would there be any allocation regarding passing the lambda to

bar

?

hello! by any chance anyone knows what might be causing the difference in the behavior of reading binary content from file?

javaClass.classLoader.getResource("myFile").readBytes()  // 198
File("myFile").inputStream().readBytes() // 184

If I'm reading input stream from a resource (which I have to in deployed app) I get some extra bytes that I do not get if I read the file directly. Any ideas?

Hi guys, the stdlib

fun List<Pair<K,V>>.toMap()

drops duplicate entries without providing a way to merge them. Is there a stdlib function that can do this? I often need this when dealing with maps containing quantities. I implement it this way:

fun <K, V> List<Pair<K, V>>.toMap(combine: (V, V) -> V?): Map<K, V> {
    val result = mutableMapOf<K, V>()
    for ((k, v) in this) {
        result.merge(k, v, combine)
    }
    return result
}

Another one I'm missing is merging 2 maps provided a function to recombine the values of keys that are present in both maps.

hi everyone. I want to know why there isn't something like

lateinit val

which is immutable after the initialization...? in my practice actually my

lateinit

is always for this immutable occasion... A friend of mine said that in the early version of Kotlin there is something like that, but then it's withdrawn. BTW, in KotlinConf 2018 Closing Panel many a speaker regarded

lateinit

as their most annoying Kotlin feature, and seems lots of audience agreed the opinion. I am wondering if this is because of the problem mentioned above...

Probably only incidental, if lateinit did not exist, the culprit would be var some: Something?. If you need a deferred val, use by lazy {}. Problem is often with injection i guess. Which is where the antagonizing of lateinit comes from i believe.

Hi, getting back into Kotlin (on the server) after being away for a while. Searching for idiomatic Kotlin examples of a basic CRUD class, without Hibernate or other ORM. Is it possible for the class to have its own .save() and .get() methods, and also to have immutable (val) internal data? (i.e. want to avoid the

var id:Int = 0

boilerplate, because once established, all values should be immutable, and no instance should ever have id = 0) Thanks 🙂

Is it possible to do a negative infix operator? I currently have this operator:

infix operator fun contains(option: Option): Boolean

I would like to be able to write both cases

if (data contains MyOption)

and

if (data !contains MyOption)

hello, a question related to SAM functional interfaces

interface RequestAuth {
    fun header(): Pair<String, String>
}
val instance = object : RequestAuth {
                override fun header(): Pair<String, String> = "name" to "value"
            }

cant this be done more more concisely? sth like

val instance = object : RequestAuth { "name" to "value" }

I want to write fast Kotlin code on on website that provides algorithm challenges with large amount of data that's something new to me any tips?

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How would you have a data class inheriting a sealed class and its variables without having to pass them, something like

sealed class Source(
    @Json(name = "value")
    val value: String,
    @Json(name = "value2")
    val value2: Boolean
) {
    object Source1: Source
    object Source2: Source
}

Hi, is this behaviour a known bug? Or is this supposed to happen?

generateSequence(0) { it + 1 }.take(100000).fold(emptySequence<Int>()) { acc, v ->
        acc + v
      }.first() => stackoverflows

Also this works fine:

generateSequence(0) { it + 1 }.take(100000).fold(emptySequence<Int>()) { acc, v ->
        sequenceOf(v) + acc
      }.first() => works fine

Hi all, coming from Swift development, I’m able to store some user defaults / persist some small items using something called CoreData (for those who’ve not heard of it). What would the equivalent be for Kotlin/Android development to persist some user data?

Is general a good place to ask about best channel for a topic that isn’t super obvious? Looking for low hanging fruit with psi https://www.jetbrains.org/intellij/sdk/docs/basics/architectural_overview/psi_elements.html. For detekt/lint stuff but also maybe intellij plugins?

Hi, someone have used kotlinx.cli ? I try to add it as dependeny but I never can use it in my code. https://mvnrepository.com/artifact/org.jetbrains.kotlinx/kotlinx-cli/0.2.0-dev-7

repositories {
    mavenCentral()
    maven { url = uri("<https://dl.bintray.com/kotlin/kotlin-dev>") }
}

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
    implementation "org.jetbrains.kotlinx:kotlinx-cli:0.2.0-dev-7"
}

fun main(args: Array<String>) {
    val parser = ArgParser() // ArgParser not found
}

Is it possible to have something like/similar to this in Kotlin? object O { fun <T> f1(param: T) { f2(param) } private fun f2(i: Int) {...} private fun f2(f: Float) {...} } O.f1(123) O.f1(123.45f)