I hate to ask this... is there a one-line way of getting the first half of a list for a forEach loop? And then the second half of the list?

I have a sealed class

Event<P>

, and a bunch of objects that inherit from the class with a few different types for

P

. I receive some json that has a name field so that I can match it to one of the objects, and data field that I want to deserialize into an object of type

P

. Is there any way to do this without doing a case-by-case when for each event type?

I was solving problems on the the ProjectEuler https://projecteuler.net/problem=11 For the 11th problem, can I simplify my code better, (idomatic): This is current version of my code (it looks ugly to me):

const val grid =
    """
    08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
    49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
    81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
    52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
    22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
    24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
    32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
    67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
    24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
    21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
    78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
    16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
    86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
    19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
    04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
    88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
    04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
    20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
    20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
    01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
    """

fun main() {
    solve()
}

private fun solve() {
    val gridLines = grid.trimIndent().lines()
        .map { line -> line.split(" ").map { it.toInt() } }
    var result = 0

    for (i in 0..gridLines.size - 4) {
        for (j in 0..gridLines.first().size - 4) {
            // going left to right
            run {
                val line = gridLines[i]
                val res = line[j] * line[j + 1] * line[j + 2] * line[j + 3]
                if (res > result) result = res
            }

            // going top to bottom
            run {
                val res = gridLines[i][j] * gridLines[i + 1][j] * gridLines[i + 2][j] * gridLines[i + 3][j]
                if (res > result) result = res
            }

            // going diagonally top-left to bottom-right
            run {
                val res = gridLines[i][j] * gridLines[i + 1][j + 1] * gridLines[i + 2][j + 2] * gridLines[i + 3][j + 3]
                if (res > result) result = res
            }

            // going diagonally top-right to bottom-left
            run {
                val max = gridLines.first().lastIndex
                val res = gridLines[i][max - j] * gridLines[i + 1][max - j - 1] * gridLines[i + 2][max - j - 2] * gridLines[i + 3][max - j - 3]
                if (res > result) result = res
            }
        }
    }

    println(result)
}

but it doesn't let me assign null to the value, because it has smart-casted it to a non-nullable!

2. is this actually a good way to write code?

.takeIf {}?.let {} ?: else

another question I have an interface Measure, with an abstract function convert(target: Measure) I have three enum classes (Length, Weight, Temperature) that implement the interface and override the convert() function I also have a String.toMeasure() extension function that parses a string as an enum of one of three classes and returns a Measure object I want each enum class to be able to convert only to another enum of the same class There are two ways to do it 1) make the convert() function take an argument of type Measure, then check if the target is of the same enum class as the source, else throw exception the downside here is that each overridden implementation of this function needs to check if source and target are of the same class (otherwise the "when" is not exhaustive) I'd like to localize the check to one place 2) I declare interface Measure<T>, with an abstract function convert(target: T) and I declare my enum classes as Length : Measure<Length>, etc this way, each enum can only convert to another enum of the same class however, this is where I get a problem with the toMeasure() function it used to return a Measure object, but now it needs to return Measure<something> continued it thread...

What is the most user-friendly way to make a GUI app in Kotlin? I heard that JavaFX was removed from the default JDK, and it means another step for the user, so what should I use?

I have this code:

val (term, definition) = string.split(" ")
val card = Card(term, definition)

I would like to do this:

val card = Card(string.split(" "))

but it appears I cannot do that not even with using the spread operator (*) am I missing some thick? or no such luck?

Is there a way to create a KClass from Java (all implementations of KClass I found so far are` internal` - so probably not intended to be used from Java)?

I have a list of strings and I want to check if my strings doesn’t contain any of the values of this list. How can I do that?

val list = listOf("ab", "cd")
val string1 = "abf"
val string2 = "xy"
print(myFunction(string1, list)) // true
print(myFunction(string2, list)) // false

I have a list like:

val list: List<Any>

How to check its type by the condition ?

when(lists){

is List<Cat> -> {

}

is List<Dog> -> {

}

}

}

Is there any way of doing this stuff? Thanks in advance.

Assuming you have a DSL like below, I want to add a condition to add +Person("Emily", 31) to the list, what would be the most suitable syntax?

val v = village {
        house {
            +Person("Emily", 31)
            +Person("Hannah", 27)
            +Person("Alex", 21)
            +Person("Daniel", 17)
        }
        house {
            +Person("Joe", 48)
        }
        house()
        house {
            -Person("Sarah", 40)
            -Person("Tom", 26)
            -Person("Holly", 52)
        }
    }

Is there a way to prevent and object from being copied outside of a lambda with receiver? If it can't be done, can I somehow hide the functions to everything outside of the lambda?

I'm trying to use a scratch file for some prototyping. In my build.gradle file, I have the flag set to allow kotlin.Result as a return type. However, that doesn't seem to apply to my scratch file. What should I specify to allow kotlin.Result as a return type in scratch files?

Noticed some odd behavior around resolving functions that I think might be a compiler bug, but maybe I’m just missing some rule that actually makes sense. If you have two functions that operate on an interface, and a sub-interface of that interface, when you pass a concrete type to this function the kotlin compiler will resolve the function with the more specific type. However, if this interface takes a type parameter, and the more general overload has a type bound (eg of

Any

), when you pass a value that satisfies the bounds, the compiler suddenly can’t figure out which one to call. So this works:

fun <T : Any> StateFlow<T>.thing(): Unit = TODO()
fun <T : Any> Flow<T>.thing(): Unit= TODO()
MutableStateFlow("").thing()

And this:

fun <T> StateFlow<T>.thing(): Unit = TODO()
fun <T> Flow<T>.thing(): Unit = TODO()
MutableStateFlow("").thing()

And this:

fun <T : Any> StateFlow<T>.thing(): Unit = TODO()
fun <T> Flow<T>.thing(): Unit= TODO()
MutableStateFlow("").thing()

But not this:

fun <T> StateFlow<T>.thing(): Unit = TODO()
fun <T : Any> Flow<T>.thing(): Unit = TODO()
MutableStateFlow("").thing()

tasks.getByName<Jar>("jar") {
    enabled = true
}

tasks.getByName<BootJar>("bootJar") {
    enabled = true
    manifest {
        attributes( "Main-Class" to "kr.co.korbit.gia.Application")
    }
    launchScript()
}

This is my bootJar configuration of kotlin SpringBoot Project: But "gradle bootJar" generate following error : FAILURE: Build failed with an exception. * What went wrong: Execution failed for task 'internalbootJar'.

Main class name has not been configured and it could not be resolved

* Try: Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights. * Get more help at https://help.gradle.org BUILD FAILED in 3s

https://twitter.com/kotlin/status/1267750314024808450 On a map, use 'withDefault' to get a wrapper that obtains a default value when using 'getValue' on a key that is not present. Note that this does not change the behavior of the indexed access operator x[idx] / x.get(idx)! https://t.co/kldivSn4mI #KotlinTips https://t.co/VM20ZtrWbi Twitter

I wonder why compiler not complaining for try/catch when we use

first()

with collections, It might throw an Exception

can someone add me to kotlin multiplatform channel?

when idea suggests to add a library to the classpath (like https://imgur.com/RxcOZ2a), where can I find the corresponding setting? I tried to commit before and later but apparently there is no change in

.idea

.. how is possible?

Hi can I ask a retrofit2 /kotlin question in this channel?

Anyeone know what this is ? I cant find any action by that name.

In retrofit2, Callabck just means that it goes back to

override fun onResponse(call: Call<List<Photos?>?>, response: Response<List<Photos?>?>) {

if it is successful and I see the dataclass fully populated. What is the most elegant way of handling on Response? SHould I pass an object in the constructor to say call a method on the passed object to populate the data?

We are starting the 1.4-M2 release activities. Please be patient, it will take a bit of time. It will be officially out only after the blog post appears in blog.jetbrains.com/kotlin. In the next couple of days you may see new artifacts appear in various repositories. Since we don’t have full control of all the systems involved, you may temporarily observe an inconsistent state of the 1.4-M2 world. Please don’t be alarmed, the blog post will notify you when we reach a consistent state 🙂 Looking forward to your feedback on 1.4-M2 when it’s ready. Have a nice Kotlin!

Hi all, I have no idea how to do the following : I have a few classes

A

,

B

,

C

, ... (for our use-case, they are describing different type of Message) I have a function

f

defined by

f(msg: A) : AP

,

f(msg: B) : BP

,

f(msg: C) : CP

... that convert those message into another format (Avro classes) My issue is that I have no way to apply this function to an arbitrary collection of

A

,

B

,

C

, ..

setOf(msgA, msgB, msgA, msgC, msgB..).forEach { f(it) }

because

it

is then of type

Any

(despite each

f(it)

individually is valid, the syntax is invalid) Would be happy to receive suggestion 🙂 about how to handle this

Which style is more idomatic, or looks/used by vast majority of community? 1.

list.map { it.toInt() }

2.

list.map(String::toInt)

3.

list.map { str: String -> str.toInt() }

Hi guys. Any idea to improve this?

val animals: List<Animal> = ....
val animalToChangeColor = animals[0]

val newColor = ....
val newAnimal = when {
    animalToChangeColor is Cat -> {
        animalToChangeColor.copy(color = newColor)
    }

    animalToChangeColor is Sheep -> {
        animalToChangeColor.copy(color = newColor)
    }

    animalToChangeColor is Dog -> {
        animalToChangeColor.copy(color = rnewColor)
    }
}

Imagine

Cat

,

Sheep

and

Dog

are data classes that implement

Animal

interface which has

color

field. It seems impossible to "polyphormise" this, but maybe i'm missing some awesome Kotlin feature 😛

Use property if… is cheap to calculate

When deciding to use property or function/method. Do you think this guideline about the calculation heaviness is significant? E.g. #1

val File.entropy: Float
    get() = TODO()

#2

fun File.getEntropy(): Float = TODO()

How can I divide a list like this? Imagine my input is:

111212221

I want my output to be:

[111], [2], [1], [222], [1]

I have a kotlin class that implements an Interface from java. When I use an object from this class as a return from a java lambda function I have type error (Cannot convert to ...) It seems like java only regconizes this object as of Object class, so it means I lose all type information?