Just discovered: https://github.com/rjaros/kvision

Can I upgrade from IntelliJ

2018.3.6

to

2019.1

without reinstalling? Can

Check Updates

do this for me somehow?

Is there any way to check if a variable is val/var?

Assign something to it, if that results in a compiler error, it’s a

val

.

Is there standard Kotlin analog of Guava

Sets.difference

? In Kotlin it will be:

fun Set<T>.difference(other: Set<T>): Set<T>
{
  return subtrack(other) + other.subtrack(this)
}

Which one would you prefer?

What’s the go to kotlin library for testing application flow? I understand how to write basic unit tests in kotlin, and also how to mock api responses, for my app, but I need something that can assert “when this button is tapped this new activity/these UI elements is/are showing on the screen”, so I guess it translates to testing navigation.

What JDK version does Kotlin support? Does it support JDK12? Would it give problems with libraries?

is there anyway to declare a parameter as modifiable without needing to do

fun a(b : Int) {
    var c = b
    c = 5
}

to be able to use kotlin contracts, do I have to use experimental flag?

Can I write contract inside an interface?

How does Kotlin support reification if it is not supported by JVM

don't people find it confusing that

Any?.toString()

returns "null" rather than actual null?

It doesn't?

x?.toString()

can return

null

,

x.toString where x:Any?

will return

"null"

instead.

is there a reflective way to copy A to B in kotlin (where A and B are different instances of different classes but share the same attributes)

how can i add an item to an AbstractList?

kotlin.collections.EmptyList cannot be cast to Kpp_gradle$1$1$1$a

fun <E> addOne(v: AbstractList<E>) {
    v.add(listOf<E>() as E)
}

class a {
    val empty : Int = 0
}

fun ret() {
    val f = arrayListOf<a>()
    f.add(a())
    println("type of f is ${f.javaClass}")
    println("type of f[0] is ${f[0].javaClass}")
    addOne(f)
    println("type of f is ${f.javaClass}")
    println("type of f[1] is ${f[1].javaClass}")
    abort()
}

I'm upgrading from coroutines 0.3.0 to a 1.x version - how do I make IntelliJ replace usages for me? I could have sworn it offered to on another project, but I'm not getting it this time around First I switched my Kotlin version to

1.3.0

(rebuilt), then coroutines to

1.0.0

, and received no offer for automatic conversion EDIT: Found an alt-enter option to fix it, nevermind

You don’t have to put it in an object. You can just do it at the top-level of a file. But do note that if they aren’t explicitly in an object/class, that Kotlin will create a class that is the filename + kt appended to it. Also,

const

will get inlined by the compiler in your Kotlin code, but will also be static so they can be accessed from Java.

is it possible to use coroutines internally, but wrap them in a future to pass the result to java?

fun myFutureFunction(): ComleteableFuture<String> {
    // convert here?
    return ... myCoroutineFunction();
}

fun myCoroutineFunction() {
    // ... do most things here
}

Generics 101: I have two interfaces that work together like this:

interface FancyConnector<T : Transcoder<I, O>> : RawHttpConnector {
    val transcoder: T

    fun send(entity: I) = sendRaw(this.transcoder.encode(entity))
    fun receive(): O = this.transcoder.decode(receiveRaw())
}

interface Transcoder<I, O> {
    fun encode(entity: I): HttpBytes
    fun decode(raw: HttpBytes): O
}

How can I make the compiler recognise the

I

and

O

type generics? Or alternatively, how can I define my interfaces so that

FancyConnector

doesn't need to know the internal types of

Transcoder

? EDIT: Imagine there is a

class IdentityTranscoder<E> : Transcoder<E, E>

. I want to be able to use it like

class MyConnector<IdentityTranscoder<Foo>>

instead of having to specify

class MyConnector<Foo, Foo, IdentityTranscoder<Foo>>

But why?

apparently i found a bug 0.0

[18:05:11] <macropreprocess> Reason:       Type 'java/lang/Object' (current frame, stack[1]) is not assignable to 'java/lang/Integer'     Current Frame:       bci: @111       flags: { }       locals: { 'java/util/ArrayList', 'java/lang/String' }       stack: { 'java/lang/StringBuilder', 'java/lang/Object', null }
[18:08:13] <Bombe> Please go back to coding C.
[18:08:13] <Bombe> Java is obviously not for you.
[18:08:13] <yawkat> macropreprocess: tf are you doing to get that error?
[18:08:13] <yawkat> can you paste youre code?
[18:08:13] <yawkat> your*
[18:08:38] <Bombe> That’s not code.
[18:36:58] <macropreprocess> yawkat: <https://bpaste.net/show/bf6b86553f0a>
[18:37:13] <macropreprocess> wait no
[18:38:27] <macropreprocess> <https://bpaste.net/show/91122a1a2a5e>
[18:38:31] <macropreprocess> yawkat: 
[18:39:49] <yawkat> yea that looks like a bug
[18:41:29] <macropreprocess> oh
[18:41:37] <macropreprocess> yay i found a bug

Given a boolean condition I want to return an object if that expression returns

true

. Is there a shorter way (in the stdlib maybe) to write the following?

someBooleanCondition.takeIf { true }?.let { "dummy-string" }

E.g. (in pseudo-code)

someBooleanCondition.ifTrue { "dummy-string" }

Anyone familiar with validation using JSR-303 annotations ? I'm not sure if this is Kotlin related but I'm having difficulties defining my annotations using interface EDIT: Workaround is to use @JvmDefault on interface method

Does anyone know how to reference the receiver in an extension function when I'm stopped in the debugger? Neither

this

nor

$receiver

seem to be it.

Are there utilities to get a minimalised version of kotlin-std and kotlin-runtime? In the sense of dead code elimination or jigsaw ?

is there a simpler way of writing this class? I feel like my coworker could just use lateinit, but I don't know if jsonproperty allows that...

I have a

build.gradle.kts

Is it possible to define annotation that is composed or inherited from other annotations?