标签：blog lang sse ber numbers res bsp exce nbsp
断言：提供了一组断言函数以用作在代码中记录和动态检查不变量的方式。
import scala.Predef._
def addNaturals(nats: List[Int]): Int = {
// assert(nats forall (_ >= 0), "List contains negative numbers")
require(nats forall (_ >= 0), "List contains negative numbers")
nats.foldLeft(0)(_ + _)
} ensuring (_ >= 0) // 这里的"_"是函数的返回值
scala> addNaturals(List(-1, -2, 2, 3))
java.lang.IllegalArgumentException: requirement failed: List contains negative numbers
at scala.Predef$.require(Predef.scala:224)
at addNaturals(<console>:50)
... 56 elided
scala> addNaturals(List(1, 2, 3, 4, 10))
res15: Int = 20
标签：blog lang sse ber numbers res bsp exce nbsp
原文地址：http://www.cnblogs.com/wwxbi/p/6274364.html
