Scala:使用foldl将列表中的对添加到地图中？

Question

我正在尝试使用foldl将列表中的对添加到地图中.我收到以下错误:

"missing arguments for method /: in trait TraversableOnce; follow this method with `_' if you want to treat it as a partially applied function"

码:

      val pairs = List(("a", 1), ("a", 2), ("c", 3), ("d", 4))

  def lstToMap(lst:List[(String,Int)], map: Map[String, Int] ) = {
    (map /: lst) addToMap ( _, _)
  }

  def addToMap(pair: (String, Int), map: Map[String, Int]): Map[String, Int] = {
      map + (pair._1 -> pair._2)
  }

怎么了？

Answer 1

scala> val pairs = List(("a", 1), ("a", 2), ("c", 3), ("d", 4))
pairs: List[(String, Int)] = List((a,1), (a,2), (c,3), (d,4))

scala> (Map.empty[String, Int] /: pairs)(_ + _)
res9: scala.collection.immutable.Map[String,Int] = Map(a -> 2, c -> 3, d -> 4)

但是你知道,你可以做到:

scala> pairs.toMap
res10: scala.collection.immutable.Map[String,Int] = Map(a -> 2, c -> 3, d -> 4)