相关疑难解决方法(0)

我对无形特征概述中显示的示例感到困惑.

object size extends Poly1 {
  implicit def caseInt = at[Int](x => 1)
  implicit def caseString = at[String](_.length)
  implicit def caseTuple[T, U]
    (implicit st : Case.Aux[T, Int], su : Case.Aux[U, Int]) =
      at[(T, U)](t => size(t._1)+size(t._2))
}

scala> size(((23, "foo"), 13))
res7: Int = 5

1. 什么是Case.Aux？
2. 为什么参数化类型是Int not String
3. 如果size(((23,"foo",123),13)),如何定义CaseTuple？

提前谢谢了

我构建了以下内容:

import shapeless._
import poly._

object Main {
    def main(args: Array[String]) = {

        object iterateOverHList extends (List ~> Iterator) {
            def apply[T](it: List[T]) = it.iterator
        }

        val x = List(1,2,3) :: List("cat","dog") :: HNil

        val xIt = x map iterateOverHList

    }
}

上面的代码很棒,非常棒.但是,我还想要更多.我想,而不是指定我的HList将包含列表,允许任何Iterable.像这样:

import shapeless._
import poly._

object Main {
    def main(args: Array[String]) = {

        object iterateOverHList extends (Iterable ~> Iterator) {
            def apply[T](it: Iterable[T]) = it.iterator
        }

        val x = List(1,2,3) :: List("cat","dog") :: HNil

        val xIt = x …