the comparison operators (>, < etc) can call directly to Java's own

compareTo

methods? They don't need Kotlin's

Comparable

interface?

Checkout this webinar on how Kotlin is making our lives as engineers easier at Intuit: http://bit.ly/Kotlinwebinar

I actually never got that message hence my question

I'm been using kotlin for more than 3 years. I always use str?.let for null checking. I read a article today and I'm confused. Doesn't this recommendation really make sense?

// NOT RECOMMENDED
fun process(str: String?) {
    str?.let { /*Do something*/   }
}

// -> decompile will get
public final void process(@Nullable String str) {
   if (str != null) {
      boolean var4 = false;
      /*Do something*/
   }
}


// RECOMMENDED
fun process(str: String?) {
    if (str != null) {
        // Do Something
    }
}

Is there a way to use `List`'s indexOf() of a list of a type on another type, for example I have a list of

Product

and

ProductToOrder

which are quite similar in terms of

id

and

name

, I overrode the`equals()` already but

productsToOrder?.indexOf<Any>(product)

always returns

-1

Is it possible to have a default argument for a function parameter (function having another function as a parameter and that function parameter has a default value just as a variable could have)?

Or you could use this:

inline fun <T> Array<Array<T>>.forEach2D(action: (T) -> Unit): Unit {
    for (array in this) for (element in array) action(element)
}

Hey folks...is it possible to get all instances of a class (

TimerTask

) at runtime and excute the

run()

method on them?

So the answer is

no

?

val x = BigDecimal.ONE
val y = x.setScale(999)

x == y // => false
x.compareTo(y) == 0 // => true

I may by blind but I dont see it, or should I just use

map

with identity function?

but a for-loop is not an expression, right?

So I'm a bit confused about generics. I have an interface like this:

interface IterableResponse {

    val data: List<T>
    val paginationInfo: More?
}

and I am getting an error "Unresolved reference T". I would like for any class that implements the interface to have a

data

property that is a list of anything - but I don't want to use

List<Any>

because I need the implementing classes to have typed Lists. Am I using generics incorrectly? What am I doing wrong?

Hi, I've two data class as follows: data class Resource( val location : String, val address: String ) data class Student( val id : Int, var userName : String, var screenName : String, var email : String, var place : Resource, var register : Instant, val timezone : TimeZone ) How to add some sample data to 'Resource' ?

Would this work?

private fun <E> Set<E>.immutable(): Set<E> = if (this is MutableSet) this.toSet() else this

Is a for-loop the only place where

in

resolves to a call to the

iterator

?

also, does a for-loop get turned into a while loop under the hood?

Are there some property delegates for computing something expensive, preferably using suspending fun?

Hi. I'm having some problems with using listpreference.setValue or setIndexValue. None of the methods that I need to alter the values of a listpreference programmatically doesn't seem to be available. My class extends Preferencefragmentcompat Thanks Stefan

I'm stuck. Applying "kotlin-dce-js" to a js project is kicking "error: duplicate target file will be created for..." on build. Google has yielded little answers. It seems as though it's trying to output two files with the same name from the node_modules to the same dir. I have failed to locate information on how or if I should configure the scope of what is processes beyond https://kotlinlang.org/docs/reference/javascript-dce.html#configuring. Any help would be appreciated.

Why when extending a type would I lose properties on it? This is my code:

fun Response<*>.createError(): Error {
    val errorBody = this.errorBody() ?: run {
        logger.error { "createError failed: null errorBody found" }
        throw ClassCastException("Null errorBody found on response")
    }

    val error = Gson().fromJson(errorBody.string(), models.Error::class.java)
    return error
}

What is happening is I am losing the contents of

errorBody

when I try to use the receiver (Response)... I've read over the docs on class extension and I don't see anything about this?

hello there, very new to Kotlin (as in, I've started today), and I'm trying to find the way to have a secondary constructor work out in the following scenario: consider a chess board position that can be represented either through (x, y) coordinates (as a multidimensional array would), or as a string such as "B4"

class Position(val x: Int, val y: Int) {
	constructor(positionCode: String) {
		// construct a position from code here
	}
}

this yields an error as the secondary constructor must call the primary one with

: this(...)

i don't see an easy way to achieve this, i could call a function in the parent call such as

this(getCoordsFromCode(positionFromCode))

but it obviously won't work as the primary one expects two ints, and I don't think you can unpack an array into a function that isn't expecting vararg i could obviously swap the constructors and have the parent constructor call be something like

this(getCodeFromCoords(x, y))

, but I was wondering if I was missing something (and I'm pretty sure I am)

Hello! I'm also starting out with Kotlin (and Android). Is there a nicer (more idiomatic) way of doing the following check than the following?

Good talk. I wonder how the suspended send function waits until the Queue has more capacity to send. Or in other words how the send coroutine is informed that the Queue has capacity available. It is usual and dangerous in Java to synchronize on a queue monitor and wait for its size to change. Then whatever consuming thread that acquires the monitor will consume some items release the monitor and notify other waiters. I guess that in coroutines, above mechanics is not used, it probably works by re-scheduling another

suspend send

coroutine in the executor. Maybe not, maybe it spins lock on the Queue capacity. The same for the counterpart

suspend consumer

Does anyone can explain what happens internally?

is it possible to change the parameter name when using

with(...) { }

? It was error-free until I changed it to

with(...) { sf -> ... }

and now IntelliJ says

Expected no parameters

Hi all, am an android developer. I want to learn server side programming, can any one suggest me where can i start ? I know nothing about server side programming.

I am encouraging my colleagues to use Kotlin, and to do Kotlin Koans. While in some cases it is fine, in some others I find some pushback asking for how long will Koans completion take. Is there some kind of ‘official’ estimation or someone could share how long it took for them to do?

Hey guys. For class delegation. Can I delegate it to a property instead of value sent from constructor ? For example instead of:

class Derived(b: Base) : Base by b {
    override fun printMessage() { print("abc") }
}

I want

class Derived : Base by b {
    late init var b:Base
    fun initB(outerB:Base){
       b = outerB
    }
    override fun printMessage() { print("abc") }
}

Is it doable?

I am trying to implement a trivial two-state state machine (turnstile) using `fun`s to implement states. First problem was that

typealias

didn’t support a recursive definition so I couldn’t do:

typealias State = (pushes: ReceiveChannel<Unit>, coins: ReceiveChannel<Unit>) -> State

So I had to resort to defining

State

as a

@FunctionalInterface

meh. With some liberal casts, this compiles but it fails at runtime (see comment above line 59): https://gist.github.com/Bill/b9cbfdb1d6fbba42258ee0a6fcee7240 Eschewing

fun

and defining the states as `object`s works but that seems like a lot of extra ceremony: https://gist.github.com/Bill/d5fa8c0290e49fccb90936745b29e86f Any ideas here?

Is there a way to do this without using mutableList?

fun Example.sequence(vararg operations: Example.() -> Example): List<Example> {
    val sequence = mutableListOf(this)
    operations.forEach { sequence.add(it(sequence.last())) }
    return sequence.toList()
}