Is it possible to create an extension function on functions?

# getting-started

[Ellen Spertus]

Is it possible to create an extension function on functions?

[Nuru Nabiyev]

Can you give an example where/how this is going to be used?

[Ellen Spertus]

Yes, I'm thinking of creating something that shows stack growth, as part of a course I'm teaching. If a function was invoked using my extension method, stack information would be displayed

[Nuru Nabiyev]

Well you can technically investigate function like this using reflection

[Nuru Nabiyev]

Or even run it like this, but I don’t think stack information is visible here.

[Nuru Nabiyev]

You will need to investigate the JVM itself on runtime

[Ellen Spertus]

Couldn't I get stack information by throwing and immediately catching an exception?

[Ellen Spertus]

In any case, I'd be happy to fake the stack information.

[Ellen Spertus]

There are probably better ways of doing what I want, such as creating a map between function names and functions that might be called and creating the extension function on that.

[Nuru Nabiyev]

The stack information is visible to JVM. I suggest for you to look into a profiler. It gives you the information in there, including thread info, stack info, created objects, etc

[Jacob]

fun (()->Unit).functionInvoker(){
    println("invoking function")
    this()
}
fun helloWorld(){
    println("hello world")
}
fun main(){
    {helloWorld()}.functionInvoker()
}

[Youssef Shoaib [MOD]]

Even better would be calling it like this:

::helloWorld.functionInvoker()

[ephemient]

Java 9 added https://docs.oracle.com/javase/9/docs/api/java/lang/StackWalker.html which is cleaner than misusing a throwable to walk the stack

[ephemient]

but it is generally not recommended to create extensions on function types in Kotlin: https://kotlinlang.slack.com/archives/CQ3GFJTU1/p1634832675000100?thread_ts=1634242183.020800&cid=CQ3GFJTU1

[Ellen Spertus]

Thanks! I think I'll give up on the idea.