为什么这个Scala行返回一个单位?

if表达式具有单位类型,因为没有else子句。因此,有时它什么也不返回(Unit),所以整个表达式都有类型Unit。

(我想你是想问为什么它不返回Int,而不是Boolean)

太 习惯用语?是的,我们可以!

Set(3,5).map(k => Set(0 until n by k:_*)).flatten.sum

丹尼尔的建议看起来更好:

Set(3,5).flatMap(k => 0 until n by k).sum

scala> val answer = (1 until 10) filter( current => (current % 3 == 0) || (current % 5 == 0)) sum
answer: Int = 23

注意过滤器而不是if。

另一个更习惯用法的Scala:

( for( x <- 1 until 10 if x % 3 == 0 || x % 5 == 0 ) yield x ) sum

object Euler {
    def main(args : Array[String]) {
        val answer = (1 until 10).foldLeft(0) ((result, current) =>
            if ((current % 3 == 0) || (current % 5 == 0))
                result + current
            else
                result
        )

        println(answer)
    }
}