Hello, I have a question about using Java 9's immutable collection factory functions in Kotlin. I w...

# stdlib

[homchom]

Hello,

I have a question about using Java 9's immutable collection factory functions in Kotlin. I want to make an immutable list (as opposed to a read-only view of a list), mainly for defensive purposes, but when I use List.of IntelliJ warns me that it "should be replaced with [the] Kotlin function" listOf. If I understand correctly, these two functions are actually very different; is there something I am missing? Is this a false positive?

[ephemient]

https://youtrack.jetbrains.com/issue/KTIJ-12411 it is an intentional part of Java-to-Kotlin conversion

[ephemient]

also, runtime-enforced immutability instead of type-enforced is not necessary in good Kotlin code, and since the Kotlin compiler doesn't know about Java semantics, it allows you to write

val x: MutableList<Int> = List.of()

whereas listOf() would be rejected

[CLOVIS]

What are you trying to defend against? The compiler will stop mutation attempts to listOf . Someone running code in the same JVM as you will be able to edit any value if they really want to.

[ephemient]

I could understand Collections.unmodifiableList() etc. being used defensively if interoperating with Java code, and List.of() is similar to unmodifiableList(listOf()) (with a few additional unique behaviors). if that really is your situation, then ignore the inspection. but if you're just in Kotlin, I would stick with the Kotlin functions.

[ephemient]

if that still doesn't satisfy you, check https://youtrack.jetbrains.com/issue/KT-9959 and https://github.com/Kotlin/kotlinx.collections.immutable/blob/master/proposal.md