Is there a comparison resource somewhere of how the JDK impacts generated Kotlin code? I'm particula...

# compiler

[CLOVIS]

Is there a comparison resource somewhere of how the JDK impacts generated Kotlin code? I'm particularly interested in changes since Java 11. Does targetting a more recent Java version change the generated code, and how?

[udalov]

At the moment, I think there are only two features which are affected by JVM bytecode target version:
1. If JVM target >= 9, string concatenation uses invokedynamic
2. If JVM target >= 17, the PermittedSubclasses attribute is written, which makes switches over Kotlin sealed classes exhaustive in Java
But there are plans to support more, e.g. KT-65688.

[mbonnin]

Did a quick search for >= JvmTarget and those were the 2 results indeed: https://github.com/search?q=repo%3AJetBrains%2Fkotlin%20%20%3E%3D%20JvmTarget&type=code

[mbonnin]

Maybe Records? https://github.com/JetBrains/kotlin/blob/df027063420af0abd48c64ef598b1c5b0b5d7b1b/[…]ns/kotlin/resolve/jvm/checkers/JvmRecordApplicabilityChecker.kt

[udalov]

Yeah, records (@JvmRecord data class) are kinda related, but not really, since they are just forbidden unless JVM target is at least 15.

[mbonnin]

Yea the user needs to opt-in but still an incentive to bump jvmTarget