map の結果をスマートに合計する

val intList = listOf(1,2,3,4)

var result = 0
intList.forEach {
    result += it
}

intList.sum()

/**
 * Returns the sum of all elements in the collection.
 */
@kotlin.jvm.JvmName("sumOfInt")
public fun Iterable<Int>.sum(): Int {
    var sum: Int = 0
    for (element in this) {
        sum += element
    }
    return sum
}