sumBy

inline fun <T> Array<out T>.sumBy(selector: (T) -> Int): Int(source)

data class Person(val name: String, val age: Int)

val people = arrayOf(
    Person("Alice", 30),
    Person("Bob", 25),
    Person("Charlie", 35)
)

val totalAge = people.sumBy { it.age }

println("Total age: $totalAge")  // Output: Total age: 90