Why doesn't sumBy(selector) return Long?

Question

sumBy(selector) returns Int

sumByDouble(selector) returns Double

Why doesn't sumBy return Long? Is there a workaround for this?

Answer 1

That's a decision Kotlin team made. Since it's not possible to have return type overloads in Java the sumBy* have to have different names depending on the return type.

It's easy enough to add your own sumByLong though:

inline fun <T> Iterable<T>.sumByLong(selector: (T) -> Long): Long {     var sum = 0L     for (element in this) {         sum += selector(element)     }     return sum }