Using exceptions as default arguments in Kotlin - function

Question

I'm writing a function in Kotlin to retrieve items of type T from a database.
The user can specify an action to be invoked if no matching results are found, otherwise an IllegalArgumentException is thrown:
fun get(
...,
onNoneFound: () -> T = throw IllegalStateException("No matching results found")
): T {
...
return when (results.size) -> {
0 -> onNoneFound.invoke()
1 -> ...
else -> chooseResult(...)
}
}
The issue I'm having is that whenever the function is invoked, it seems that the IllegalStateException is thrown before the function body is executed.
In a way, that makes sense, and I suppose a workaround could be:
fun get(
...,
onNoneFound: (() -> T)? = null
): T {
...
return when (results.size) -> {
0 -> if (onNoneFound == null) {
throw IllegalArgumentException("No matching results found")
} else {
onNoneFound.invoke()
}
1 -> ...
else -> chooseResult(...)
}
}
I was wondering if there is a more elegant/preferable solution to this problem - ideally where I do not have to make the function nullable and do a null check later. Is there a way of doing this with Kotlin's default argument syntax?
Edit:
It occurred to me that I can use the elvis operator for the null check which does make the code more elegant:
onNoneFound?.invoke() ?: throw IllegalArgumentException("No matching results found")
But I'm still curious if Kotlin has a built-in way of doing this without the null check.

Answer 1

You shouldn't build the exception directly. Try:
fun get(
...,
onNoneFound: () -> T = { throw IllegalStateException("No matching results found") }
): T {
...
return when (results.size) -> {
0 -> onNoneFound.invoke()
1 -> ...
else -> chooseResult(...)
}
}

Answer 2

The problem is that throw IllegalStateException(...) is a perfectly fine expression of type () -> T, just as it is an expression of any other type; but it throws the exception immediately, what you want is a lambda which will throw the exception when invoked. And that's { throw IllegalStateException(...) } in Kotlin, as
Roger Lindsjö's answer says.