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  • v

    v79

    05/30/2020, 7:43 PM
    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?
    b
    a
    • 3
    • 4
  • a

    Andrew

    05/30/2020, 8:57 PM
    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?
    j
    d
    +3
    • 6
    • 12
  • a

    Animesh Sahu

    05/31/2020, 6:42 AM
    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)
    }
    b
    • 2
    • 1
  • m

    mplain

    05/31/2020, 10:48 AM
    but it doesn't let me assign null to the value, because it has smart-casted it to a non-nullable!
    k
    • 2
    • 1
  • m

    mplain

    05/31/2020, 10:50 AM
    2. is this actually a good way to write code?
    .takeIf {}?.let {} ?: else
    :yes: 1
    🤢 4
    :thread-please: 4
    :no_red: 2
    a
    k
    m
    • 4
    • 10
  • m

    mplain

    05/31/2020, 12:01 PM
    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...
    k
    • 2
    • 9
  • s

    StragaSevera

    05/31/2020, 4:20 PM
    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?
    d
    r
    +2
    • 5
    • 9
  • m

    mplain

    05/31/2020, 5:22 PM
    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?
    m
    s
    m
    • 4
    • 8
  • r

    robstoll

    05/31/2020, 7:54 PM
    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)?
    s
    • 2
    • 1
  • a

    ahmad

    05/31/2020, 10:08 PM
    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
    d
    • 2
    • 2
  • a

    Aslam Hossin

    06/01/2020, 1:59 AM
    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.
    j
    d
    • 3
    • 3
  • i

    iguissouma

    06/01/2020, 12:48 PM
    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)
            }
        }
    g
    e
    +2
    • 5
    • 11
  • c

    Chilli

    06/01/2020, 3:03 PM
    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?
    Untitled
    m
    s
    • 3
    • 5
  • s

    Steve

    06/01/2020, 9:14 PM
    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?
    f
    • 2
    • 2
  • z

    Zach Klippenstein (he/him) [MOD]

    06/02/2020, 12:19 AM
    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()
    m
    • 2
    • 5
  • m

    Mgkaki

    06/02/2020, 6:33 AM
    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 ':internal:bootJar'.
    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
    t
    p
    • 3
    • 2
  • u

    user

    06/02/2020, 9:30 AM
    message has been deleted
    🤘 4
    👍 11
    m
    • 1
    • 1
  • n

    Nav Singh

    06/02/2020, 9:34 PM
    I wonder why compiler not complaining for try/catch when we use
    first()
    with collections, It might throw an Exception
    z
    c
    h
    • 4
    • 10
  • m

    Mananpoddarm

    06/03/2020, 5:16 AM
    can someone add me to kotlin multiplatform channel?
    p
    • 2
    • 2
  • e

    elect

    06/03/2020, 10:45 AM
    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?
    m
    t
    n
    • 4
    • 4
  • r

    Regan Russell

    06/03/2020, 11:34 AM
    Hi can I ask a retrofit2 /kotlin question in this channel?
    a
    • 2
    • 1
  • s

    spand

    06/03/2020, 12:19 PM
    Anyeone know what this is ? I cant find any action by that name.
    e
    b
    c
    • 4
    • 8
  • r

    Regan Russell

    06/03/2020, 12:19 PM
    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?
    a
    • 2
    • 4
  • s

    stanislav.erokhin

    06/03/2020, 3:22 PM
    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!
    :kotlin-flag: 5
    👍 22
    🎉 18
    l
    • 2
    • 1
  • g

    Gilles Barbier

    06/03/2020, 5:17 PM
    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
    a
    s
    m
    • 4
    • 18
  • a

    Animesh Sahu

    06/03/2020, 5:17 PM
    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() }
    🥇 15
    2️⃣ 4
    m
    • 2
    • 3
  • z

    zkeme

    06/03/2020, 5:51 PM
    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 😛
    c
    a
    • 3
    • 6
  • n

    nil2l

    06/03/2020, 6:12 PM
    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()
    2️⃣ 2
    1️⃣ 1
    s
    s
    m
    • 4
    • 18
  • n

    nwh

    06/03/2020, 7:04 PM
    How can I divide a list like this? Imagine my input is:
    111212221
    I want my output to be:
    [111], [2], [1], [222], [1]
    d
    n
    +4
    • 7
    • 27
  • n

    NurBahnhof

    06/03/2020, 8:48 PM
    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?
    • 1
    • 1
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Title
n

NurBahnhof

06/03/2020, 8:48 PM
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?
Ok i found the reason why. My class file has a variable that is top level. So I'm actually calling a static class
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