Programming language Kotlin 1.8 cuts out old habits and expands debugging

JetBrains has officially announced the release of Kotlin 1.8, after the current release of the programming language was published on GitHub in December. New features include a new compiler parameter that disables optimizations to make debugging cleaner. There are also two experimental functions to recursively delete or copy directories.

Kotlin 1.8 also gets rid of two legacy issues. On the one hand, the old backend, which has been deprecated since version 1.5, is no longer available. At the time, JetBrains had stabilized a new common middle layer for all Kotlin’s multi-platform targets, i.e. the Java Virtual Machine (JVM), JavaScript and native applications, with the JVM IR (Intermediate Representation) backend.

Away with the ancient JDKs

On the other hand, Kotlin 1.8 no longer works with the outdated JVM targets 1.6 and 1.7, i.e. JDK 6 and 7 respectively. The standard libraries of the language are now compiled uniformly for JDK 8. so far were kotlin-stdlib, kotlin-reflectand kotlin-script-* compiled for JDK 6. If you needed the variants for a more up-to-date JDK, you had to explicitly use the Dependency kotlin-stdlib-jdk7 or kotlin-stdlib-jdk8 indicate. These entries should now be consistent through kotlin-stdlib be replaced.

The performance of the function has probably proved to be a positive side effect typeOf() in kotlin-reflect significantly improved, since caching is no longer internal, but via ClassValue he follows.

Compiler parameters for debugging

A new parameter causes the compiler to omit certain optimizations to make the code easier to debug. Deactivated in the first step -Xdebug only the so-called “Was Optimized Out” feature for coroutines, which uses variables in conjunction with potentially blocking functions (suspend Functions) optimized.

Currently still marked as experimental are the recursive deletion and copying of directories via deleteRecursively() respectively copyToRecursively() as extension functions for java.nio.file.Path. Details on enabling the experimental feature and error handling can be found in the Kotlin documentation.

Interaction with Apple languages

Kotlin/Native for applications without a JVM brings a few additions that are primarily aimed at connecting to Swift and Objective-C. The newly introduced annotation @ObjCName allows you to define your own name for Swift or Objective-C beyond the Kotlin name for functions and methods, among other things, as the following example from the Kotlin documentation shows:

@ObjCName(swiftName = "MySwiftArray")
class MyKotlinArray {
    @ObjCName("index")
    fun indexOf(@ObjCName("of") element: String): Int = TODO()
}

// Usage with the ObjCName annotations
let array = MySwiftArray()
let index = array.index(of: "element")

The also new annotation @HiddenFromObjC completely hides a Kotlin declaration from the Objective-C API. Finally get oriented @ShouldRefineInSwift to Apple’s macro NS_REFINED_FOR_SWIFT for functions in which a wrapper in Swift should replace the original declaration. The Kotlin annotation ensures that a function as swift_private is marked.

Other innovations in Kotlin 1.8 can be found on the Kotlin blog. The full list of changes can be found in the GitHub repository.

(rm)