sumByDouble

inline fun <T> Sequence<T>.sumByDouble(selector: (T) -> Double): Double(source)

data class Employee(val name: String, val salary: Double)

val employees = listOf(
    Employee("Alice", 5000.0),
    Employee("Bob", 6000.0),
    Employee("Carol", 7000.0)
).asSequence()

val totalSalary = employees.sumByDouble { it.salary }
println("Total salary: $totalSalary")