Unexpected behaviour found in K/N: ``` val r = At...

# kotlin-native

[Arkadii Ivanov]

Unexpected behaviour found in K/N:

val r = AtomicReference(1000L)
val v = r.value
println(r.compareAndSet(v, 2000L))

The code above prints false. Line val v = r.value unboxes the value so compareAndSet is called with new instance of Long and fails. I am aware of AtomicLong, I'm trying to write some inline extensions for AtomicReference and they fail if type T is primitive.

[Dominaezzz]

It's boxed again, so object is different.

[Dominaezzz]

And seeing the size of that number, the object won't be recycled.

[Arkadii Ivanov]

Yep and this is unexpected

[Arkadii Ivanov]

Since same code works fine on JVM

[Arkadii Ivanov]

The actual type of the variable v is Long in JVM

[Arkadii Ivanov]

For me it looks like a bug in compiler, there is no reason to unbox the value.

[olonho]

There’s no such code in JVM, K/N atomics are different. Code above makes not much sense in Kotlin, as primitive types got no identity and CAS relies on identity.

[svyatoslav.scherbina]

The actual type of the variable v is Long in JVM

No, it is Long!, which is still boxed.

Since same code works fine on JVM

Try this:

val r = AtomicReference(1000L)
val v = r.get()!!
println(r.compareAndSet(v, 2000L))

[svyatoslav.scherbina]

Or this:

val r = AtomicReference(1000L)
val v: Long = r.get()
println(r.compareAndSet(v, 2000L))

[Arkadii Ivanov]

This is exactly what I'm talking about. And the type is Long! because AtomicReference is the Java class not Kotlin. The following code prints false in all platforms:

fun bar() {
    val pair = 1000L to "abc"
    val value = pair.first
    foo(pair.first, value)
}

fun foo(a: Any, b: Any) {
    println(a === b)
}

The question now is why compiler unboxes the value and how we can prevent it? In Java there are different types, in Kotlin it's just Long.

[svyatoslav.scherbina]

You can use Long? in Kotlin.
Generally Kotlin doesn’t guarantee anything about identity of primitive types.