Hi!! I’ve tried to implement a Builder pattern design in Kotlin but on internet find a different ways to do. Does anyone have an idea the best way to implement one? 😬 Thanks!!!

Hi, I want to execute N tasks in a pool of K coroutines. How can I do that? I mean:

val todos = (0..1000000).map { payload -> someTaskBuilder(payload) }
// On runtime JVM will try to execute as much as it can at the same time.
val results = todos.map { task -> async { task() } }.awaitAll()
// But I want to confine total amount of running coroutines here.
// Something like this:
coroutineScope ( someContextWithCoroutinesLimit ) {
   /* todos execution */
}

Maybe I want something strange. The reason why I want that is an external system which does some work during task execution. And that external system has Connection Limit. I could fix that by using some Pool. But I was wondering is it possible to limit somehow coroutines amount in easy way.

I need a structure <K, V> where I can easily retrieve either the V given K as usually and viceversa. I used a

MutableMap

till now, but it's quite ugly to extract the K given the V (I can loop on the whole

entries

and get the first match). Is there anything better for my case?

Quick question.. I am new to Kotlin and I am wondering can anyone tell me the use of the componentN function in data classes? For example

data class Person(val firstName: String ="Demetrious", val lastName:String = "Robinson")

val person1 = Person()

println(person1.component1()) // "Demetrious"

I don't see the use of that as it only returns the value and not the property name. Wouldn't it be simpler to just write

println(person1.firstName)

/**
 * Infinite loop that reads this atomic variable and performs the specified [action] on its value.
 */
public inline fun <T> AtomicRef<T>.loop(action: (T) -> Unit): Nothing {
    while (true) {
        action(value)
    }
}

ummm I am confused... why would anyone use this? Why not just

AtomicRef#value

? (in regards to https://github.com/Kotlin/kotlinx.coroutines/blob/69c26dfbcefc24c66aadc586f9b5129894516bee/kotlinx-coroutines-core/common/src/sync/Mutex.kt#L146-L155)

out of curiosity i’ve started peeking into the kotlin byte code again. This time though ive been noticing some off behavior when decompiled back to java. Notice the random boolean declarations that are not used, these are littered throughout, anyone have any insight their use may be?

@NotNull
   public final List makeCachedVendorList(@Nullable Integer size) {
      int var2 = size != null ? size : TestDataFactory.INSTANCE.randomInt(1, 15);
      boolean var3 = false;
      boolean var4 = false;
      ArrayList var5 = new ArrayList(var2);
      boolean var6 = false;
      boolean var7 = false;
      int var15 = 0;

      for(int var8 = var2; var15 < var8; ++var15) {
         boolean var10 = false;
         int var12 = false;
         CachedVendor var14 = makeCachedVendor$default(INSTANCE, 0, 1, (Object)null);
         var5.add(var14);
      }

      return (List)var5;
   }

Is there a way to achieve the same thing, though? Overwrite the object we're attached to?

is it possible to implement the specification pattern in kotlin? as i tried https://dzone.com/articles/java-using-specification but i get the following undefined references: Predicate CriteriaBuilder Root

also does anyone know how to correctly accomplish combinators,

combinator(val).and(val).and(val).and(val) ...

as at this point the only thing i can think of is to implement it as a linked list but i already use the functions provided by the linked list implementation in

combinator

val i = input("1234") // i.value is set to "1234"
val combinator = i.combinator("12")
if (
    combinator.peek() // if "1234" starts with "12"
) {
    combinator.pop() // i.value is now "34" from "1234"
}

this is my current attempt at making such https://pl.kotl.in/1p-y2OEJA (using a binary tree or similar) which currently fails with

n4 it.value = 1
n4 it.value = 2
n5 it.value = 1
n5 it.value = 3

instead of

n4 it.value = 1
n4 it.value = 2
n5 it.value = 1
n5 it.value = 2
n5 it.value = 3

for

fun main() {
    val tree = Tree()
    val n1 = tree.Node(1)
    val n2 = tree.Node(2)
    val n3 = tree.Node(3)
    val n4 = n1.append(n2)
    val n5 = n4.append(n3)

    n1.forEach { println("n1 it.value = ${it.value}") }
    n2.forEach { println("n2 it.value = ${it.value}") }
    n3.forEach { println("n3 it.value = ${it.value}") }
    n4.forEach { println("n4 it.value = ${it.value}") }
    n5.forEach { println("n5 it.value = ${it.value}") }
}

if I am ever taking in a

List

and expect the contents to be the same, I should create a copy, right? (since the

List

might also be Immutable) ... is there any good way to only copy if it is mutable or would that be too much of a micro-optimization?

is it possible to have a list that accepts only X or Y type and not

Any

Is there an equivalent to a bytestream in kotlin? I see byte array, but the file I’m working with may be arbitrarily large. I’d like to be able to read data with different sizes (Reading a java class file, where values can be 2 bytes, 4 bytes, etc)

Hello! Who know, does exists slack channel special for kotlin-multiplatform ?

Hi, I want to get a binary representation of an object. The easier way I found was this one:

val file = File("temp")
ObjectOutputStream(FileOutputStream(file)).use { it.writeObject(obj) }
return file.readBytes()

However, I really want to avoid using files. So, I'm wondering whether there is a better/shorter way to achieve the same result. Thanks 🙂

this would be a correct implementation of

and

and

or

right? (not including combinations and association, eg

A and B or C

>

(A and B) or C

or

A and (B or C)

)

fun peek(): Boolean = if (list.size != 0) peekMultiple() else peekSingle()

// private fun peekSingle omited

private fun peekMultiple(): Boolean {
    val listTmp = cloneList(list).iterator()
    if (list.all { it.type == operatorAnd }) {
        var matches = 0
        val max = list.size
        while (listTmp.hasNext()) {
            val stackTmp = listTmp.next().once!!
            if (stackTmp.peek()) {
                matches++
                stackTmp.pop()
            } else break
        }
        if (matches == max) return true
        return false
    } else if (list.all { it.type == operatorOr }) {
        while (listTmp.hasNext()) if (listTmp.next().once!!.peek()) return true
        return false
    }
    else return false // unsupported operator or combination of different operators
}

infix fun and(right: IsSequenceOnce): IsSequenceOnce {
    val stackTmp = parent.clone().IsSequenceOnce(this.value)
    if (this.list.size != 0) stackTmp.list.addAll(this.list) else stackTmp.list.add(Types().also { it.add(this, operatorAnd) })
    if (right.list.size != 0) stackTmp.list.addAll(right.list) else stackTmp.list.add(Types().also { it.add(right, operatorAnd) })
    return stackTmp
}

infix fun or(right: IsSequenceOnce): IsSequenceOnce {
    val stackTmp = parent.clone().IsSequenceOnce(this.value)
    if (this.list.size != 0) stackTmp.list.addAll(this.list) else stackTmp.list.add(Types().also { it.add(this, operatorOr) })
    if (right.list.size != 0) stackTmp.list.addAll(right.list) else stackTmp.list.add(Types().also { it.add(right, operatorOr) })
    return stackTmp
}

for example,

val E = parseStream.IsSequenceOnce("E")
    val F = parseStream.IsSequenceOnce("F")
    val FE = F or E
    val EF = E and F
    println(EF.peek())
    println(FE.peek())

By default yes https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/lazy.html#

default thread-safety mode LazyThreadSafetyMode.SYNCHRONIZED.

Locks are used to ensure that only a single thread can initialize the Lazy instance.

How do I use setAudioattribures instead of setAudioStreamtype

is it possible to make

val x: Stack<String> = "a"

auto convert to

return Stack("a")

via some function without needing to explicitly state

val x = Stack<String>("a")

This message was deleted.

is it possible to have multiple

infix

functions in a chain? for example,

true and not false

where

and

and

not

are

infix

functions

Is there a way to reference

self

or something equivalent in a constructor of a data class such that you could do something like:

abstract class A(abstract name: String?)

data class B(override val name: String? = self::class.simpleName): A()

val b = B()
print(b.name)        // B

Good afternoon, I'm new to Kotlin and working through a Big Nerd Ranch book, I came across the function in their code and it isn't working, can someone help me with the solution.val healthStatus = when (healthpoints) { in 100..89 -> EXCELLENT_HEALTH in 90..99 -> GOOD_HEALTH in 75..98 -> MINOR_HEALTH in 75..89 -> if (isBlessed) {IS_BLESSED } else { } in 15..74 -> LOW_HEALTH else -> POOR_HEALTH } ... println("$name $healthStatus")isBlessed is set to true, and I have a string stored in const val IS_BLESSED. The issue I am having is that string is not printing regardless the range of the healthpoints.

I’m trying to get model extensions defined on an interface to only be accessed via the implementations of the interface. Unfortunately, it looks like within lambdas being passed to the implementations, the context required to actually use the extensions is not fulfilled. Here is an example of what I’m trying to do: https://pl.kotl.in/byJT79Q0W A quick summary:

interface Foo{
  fun createContext(action: MyObject.() -> Unit)
  fun MyObject.makeChange()
}

myObject.makeChange() //this should be illegal
myFoo.createContext {
  makeChange() //this should be legal
}

Is there a way to achieve what I’m attempting?

I suppose I am asking for further help understanding when expressions. In the above code snippet, not only does IS_BLESSED (line 40) not print, but "UNKNOWN RACE" in line 25 always prints. But if race is assigned to orc, and the when expression checks for race, why doesnt it print HILL_PEOPLE?

is there a not so verbose way to define a class that contains all the fields from another + a new one (I don't care if it's via inheritance, composition)

I'm modelling notification objects. The "default" ones, with name, description and so on, and then I have "progress" notifications which have everything contained in the "default" ones + a field for a message when the process is complete

working with generic numbers of type

N : Number

. If I have a comparison shall I cast

if((v as Int) == (vCur as Int))

or I can leave it plain

if(v == vCur)

?