How to overload operator for null?

Question

I would like to overload an operator like invoke for null literal.

For example, so I could writen something like

null(1, 2)

Is it possible?

Answer 1

I wouldn't advise overloading anything on the null literal, as it would cause too much confusion and would have no real-world use case.

However, technically, it's possible:

operator fun Nothing?.invoke() = "hi!"

fun main() {
    println(null())  // Works, prints "hi!"

    val x = null
    println(x())  // Also works.

    val y: String? = null
    //println(y())  // compilation error

    val z: String = ""
    //println(z())  // also compilation error
}

It makes use of the fact that the null keyword has the nullable type Nothing?.