Scala - value < 不是 AnyVal 的成员

Question

这是我的代码。我在第二个 case 子句中遇到编译错误:

Error:(92, 26) value < is not a member of AnyVal case x if x._2 < 2 => "price under 2"

def tupleMatch: Unit = {
  val donut = Tuple2("Donut", 2.5)
  val plain = Tuple2("Plain", 1.0)
  val tuples = List(donut, plain)
  tuples.foreach { tuple => 
    val toPrint = tuple match {
      case ("Donut", price) => s"price of Donut is ${donut._2}"
      case (_, price) if price < 2 => "price under 2"
      case _ => "other"
    }
    println(toPrint)

  }
}

我改变后

val plain = Tuple2("Plain", 1)

到

val plain = Tuple2("Plain", 1.0)

它终于起作用了。
这让我很困惑，我想知道为什么？

Answer 1

那是因为您的元组数组由两种不同的类型组成:Tuple2[String, Int]和 Tuple2[String, Double] .这些类型由编译器推断，然后元组数组的干扰类型是 Tuple2[String, AnyVal] .当您放置 Double 表示时，编译器能够创建 Tuple2[String, Double] .