相关疑难解决方法(0)

看着

val sb = Seq.newBuilder[Int]
println(sb.getClass.getName)
sb += 1
sb += 2
val s = sb.result()
println(s.getClass.getName)

输出是

scala.collection.mutable.ListBuffer
scala.collection.immutable.$ colon $ colon

使用Scala 2.10.1.

我希望Seq.newBuilder能回来一个VectorBuilder例子.这是由返回CanBuildFrom,如果结果是显式类型的Seq:

def build[T, C <: Iterable[T]](x: T, y: T)
                              (implicit cbf: CanBuildFrom[Nothing, T, C]): C = {
  val b = cbf()
  println(b.getClass.getName)
  b += x
  b += y
  b.result()
}

val s: Seq[Int] = build(1, 2)
println(s.getClass.getName) // scala.collection.immutable.Vector

在这种情况下,构建器是a VectorBuilder,结果的类是a Vector.

所以我明确地希望构建一个Seq,但结果是 …