I tried lambda expression in Kotlin (1.5.10) with target Java 1.8. I set the compiler option -Xlambdas=indy in maven pom file. But, in Java bytecode, it still uses the wrapper class but not the invokedynamic.
And also documentation states that SAM by default uses invokedynamic (from 1.5). But, I checked, it still creates a wrapper class.
Could you please let me know, where I am going wrong?
Thanks
My Example code
fun interface Vehicle {
fun start()
fun stop() {
println(“Vehicle is stopped”)
}
}
fun main() {
val vehicle = Vehicle { println(“Car is started”) }
vehicle.start()
vehicle.stop()
}
Try a normal lambda instead of a fun interface, because fun interfaces are compiled as wrapper classes because they specifically have to implement that interface AFAIK, although I think there’s plans to change that.
Edit: fun interfaces, according to the Kotlin docs, should use indy by default since 1.5.10:
SAM adapters via invokedynamic
Kotlin 1.5.0 now uses dynamic invocations ( invokedynamic ) for compiling SAM (Single Abstract Method) conversions:
I found the problem. My example was not a pure Kotlin functional interface, because it contains two methods one abstract and one default implementation. I tried with the pure Kotlin functional interface and by default, it generates the bytecode with “invokedynamic”. Below is the example. And for the lambda, with just -Xlambda=indy compiler options is enough to generate the bytecode with “invokedynamic” for the lambda expression. (Initially, it did not generate, I am not sure why, but after that, I removed OptIn compiler options, and after I compiled using “mvn clean” command it worked)
fun interface Vehicle {
fun start()
}
fun main() {
val vehicle = Vehicle { println(“Car is started”) }
vehicle.start()
}
