How to serialize a lambda in kotlin

Question

I am trying to serialize a lambda as in java 8 which is performed like this:

Runnable r = (Runnable & Serializable)() ->{doSomething();};

but when it try the same thing in kotlin like this:

val r = { doSomething() } as (Runnable , Serializable)

i get a compile error of:

even if i try to paste the java code into kotlin file it will remove the serializable portion of the cast. therefore how to serialize lambda in kotlin ?

Answer 1

Kotlin lambdas are serializable by default, see https://discuss.kotlinlang.org/t/are-closures-serializable/1620.

So this will work:

 val r = { println("Hallo")} as java.io.Serializable

If you really need a Runnable then this does not work, because Kotlin creates only a Runnable instance:

 val r = Runnable { println("Hallo")} as java.io.Serializable

In this case you have to explicitly create an object:

val r = object: Runnable, java.io.Serializable {
    override fun run() :  Unit {
        println("Hallo")
    }
}