Kotlin allow changing the captured variables inside the lambda expression, unlike in Java (where captured variables are force to be final). So I think by default, variables are captured by reference.

"A lambda expression or anonymous function (as well as a local function and an object expression) can access its closure, i.e. the variables declared in the outer scope. Unlike Java, the variables captured in the closure can be modified:" It doesn't explicitly state how Kotlin capture outside variables. So I can't be sure about this. It just says outside variables can be modified inside Kotlin's lambda

If Kotlin has a language specification, it would be easier to understand the magic Kotlin does.

In not-inline lambdas Kotlin uses mutable

ObjectRef

(

IntRef

,

ByteRef

, etc) to hold changing value. In IDE, when your mouse pointer is over such variable, you can see a tooltip explaining this.

@miha-x64 ok, I tried also this

fun main(args: Array<String>) {
    val pool = Executors.newFixedThreadPool(4)

    val length: Int = 10000
    var startIndex: Int = 0
    var endIndex: Int = length

    for (i in 1..4) {
        pool.execute { task(startIndex, endIndex) }
        startIndex = endIndex
        endIndex = if (i < 4 - 1) endIndex + length else 40000
    }

    pool.shutdown()
}

inline fun task(start: Int, end: Int) {
    println("Start: $start; End: $end")
}

and it almost works fine but it is possible to get this output:

Start: 10000; End: 20000
Start: 10000; End: 20000
Start: 20000; End: 30000
Start: 30000; End: 40000

oh sorry, now I understand but what is the elegant way to achieve this goal?

Calculate start and stop index from i, not sharing them between threads

ok sounds reasonable:) but is there a way to use primitives instead of wrapping to reference

Can't​ test it now. But how about copying the indices into vals, before execute(), and then using the copies inside the closure

yea I have done it in order to make it work

but it seems strange for me

Well, it is a classical race. You are modifying shared variables.

Sometimes you read them before modification, sometimes after

of course, but if those variables would be primitives that would be ok to use them like that

and as the guy said: "In not-inline lambdas Kotlin uses mutable

ObjectRef

(

IntRef

,

ByteRef

, etc) to hold changing value. In IDE, when your mouse pointer is over such variable, you can see a tooltip explaining this."

No, it wouldn't. Being primitives or not has nothing to do with this. Being modifiable from outside the closure is what's causing the problem here.

yes

If Java would allow non-final captured variables it would have the same behavior, no matter if the captured variable was boxed or a primitive.

primitive is not reference so it couldn't be modified when it were passed

But you're not passing the primitive anywhere, this isn't a function call - you're simply accessing the same variable from different places.

Look at it as if you had a class around your code and the indices were members

You would get the same result

Consider this code:

var x = 0
repeat(10) { x += 1 }

After this code block,

x

will be

10

. If the code behaved like you seem to be expecting,

x

would still be

0

after the block, which negates all the benefits you get by having real closures.

Thank you, now I see where I was wrong:)

Newbie with a question... I have a java based third party library that uses Java Reflection to grab all of the methods on a class that I provide to it. the issue is that the Third party code is using reflection to do a class.getMethods() which is problematic because the class is in Kotlin and has now "hidden" those fields

@usernamewastaken could you please describe the problem more specifically?

Usually there are no problems with java reflection on kotlin classes because there is not much difference between kotlin byte code and java byte code

class is in Kotlin and has now "hidden" those fields

What fields did you mean?

@reinhard_codes has left the channel