For some reason I can't use Java classes from my Kotlin files in IntelliJ (with Gradle). Using Kotlin from Java is fine but when I try to use a Java class it reports unresolved reference. The import quickfix of course appears but doesn't do anything. Any ideas what the problem could be? (The classes are all in the test module in case that matters)

It's not that uncommon tho. You have a set of items that share common properties and differ by one field. The result of modeling this will be quite chatty.

Hi guys, i want to know if has something in contracts that make this works

can anyone tell me how to navigate this 2d array:

var board = Array(row,{IntArray(col)})

I published Tail Call optimization in JVM with Kotlin . JVM doesn't support Tail Call optimization. But with Kotlin you can write Tail Call optimised way . This article also tells how Kotlin does this https://medium.com/@rohanmaity/tail-call-optimization-in-jvm-with-kotlin-ebdf90b34ec9

Is there any library/annotation processor out there that generates code to read some configuration bean from environment & command line args ? Something similar to @ConfigurationProperties in Spring but at compile time. I know Micronaut does something like that but I don't think there is a separate library that I can just use on a non micronaut project.

Is this behaviour documented anywhere? Why does reallyReallyReallyLong become zero? Does the result after multiplication simply get truncated to 64 bits?

Is this a Kotlin related error (I'm getting it in the Intellij Ultimate debugger evaluator while running a Kotlin expression using a Java lib), and what could this be:

An exception occurs during Evaluate Expression Action : com.sun.tools.jdi.ClassTypeImpl cannot be cast to com.sun.jdi.ArrayType

?

How can I find what intrinsics are included in construtor to check if is not-null?

Hi there, if I have the following code:

val f: (Context) -> View = ::TextView
        val text = f(activity)

how do I check that

text

is an 'instance' of

f

?

is there a bug with kapt and

abstract var

properties? I have this:

sealed class Tag<T> { // note: TagId/SongId classes are inline
    abstract var id: TagId
    abstract var songId: SongId
    abstract var data: T
}

but it only generates a setter for

data

. the other two only have getters

Can I get help with pdfs I can start with to learn kotlin... Many thanks.. 😃

First: yes, the Java class your extension functions end up in will change name. Second: no, those generics are erased anyway.

You can specify the java class name associated with the file using a file annotation

Is there a nice pattern to avoid unnecessary null checks, like following?

@Entity class MyEntity(val id: Long?, ...)
val myEntity = myEntityRepository.getById(1L)
// fun useMyEntityId(id: Long) {...}
useMyEntityId(checkNotNull(myEntity.id)) // check here is logically unnecessary, since entity retrieved from database will always have id

I'm asking in general, but if there is anything specific for Spring Boot and Hibernate, that would be also interesting.

The other way to express this is with generics,

class Entity<D: Int?>(val id: D)

and then keep the nullability in the type throughout the code.

yes, id is null before entity is persisted, but when retrieved from repository, that is impossible. So far I came up with this design:

@Entity
class MyEntity {
	@Id
	private val _id: Long? = null
	@Transient
	val id: Long
		get () = checkNotNull(_id) { "Should not try to retrieve ID of an entity before it is persisted" }
}

lateinit

doesn't work with primitive types anyway

Man, just add a boolean flag. The entity stuff is just way overcomplicating.

var hasId: Boolean = false
var id: Long = 0L
  get() = TODO()

It says in the kapt documentation: "Note that Kapt does not support multiple rounds for the generated Kotlin files." Does this mean that annotation processing won't run on them at all? Or that it will just happen once

Quick poll when you know for sure that something is not null, while it appears nullable, which construct should you use? 1️⃣ checkNotNull(something) 2️⃣ something!! If you have an explanation for your preference I encourage you to post it as a thread comment. Example:

// hibernate is used for illustration, because it recommends to use nullable IDs for entities
val entity: MyEntity = hibernateRepository.requireEntityById("some-id")
private fun String.doSomethingWithId()
// 1
checkNotNull(entity.id).doSomethingWithId()
// 2
entity.id!!.doSomethingWithId()

One more thing which I use more often than 1:

val entity = hibernateRepository.getEntityById("some-id") ?: error("some-id is null")

How do I get

KClass

from

KType

?

Hi all!! anyone could help me? what is the meaning of ! in a function param declaration? like this fun foo(param:String!)

Is there a size limit to shareable snippets in the Kotlin playground? I'm getting nothing when I try to generate a sharing link.

https://gist.github.com/andrewgazelka/b8170e452fa3dd0c0fb6d3875dc502ee think it is appropriate to have

getMemoryUsed()

outside the class as it functions as a util fun?

ummmmm

so I'm making a chess game and I've got the Rook and pawn's move function ready but I'm having some problem with the Knight's move function.

for(m in 0..(8-x))
                        for(n in 0..(8-y)) {
                            if(board.board[m][n].group != this.group) {
                            }
                        }

All I want is that the 2d array should have the ability to increase or decrease its row and column....without a for loop. Thnx

<!here> Thank you all for taking part in nominating the Most Helpful Slack Member. The final nominees are below. Please vote for your candidate using the corresponding number (you can only vote for a single candidate). Voting ends 28th December 12 pm CET. 1. @gildor 2. @jw 3. @louiscad 4. @karelpeeters 5. @Shawn 6. @kpgalligan 7. @thomasnield 8. @edvin 9. @irus 10. @raulraja