scala - 将模式匹配混合到一系列映射和过滤器中

Question

假设我想做类似下面的事情，我在其中操作一个 Scala 列表，然后执行匹配以转换为一个选项。有没有一种方法可以在不添加括号的情况下继续链(对于更复杂的示例，嵌套括号可能看起来很困惑)？

  def foo: Option[Int] = {
    MyUtils.myListOfFoo
      .flatMap(_.barList)
      .filter(_.isGood)
      .toList match {
        case List(bar) => Some(addr)
        case _         => None
      }
      .map(_.getBaz) // would like to do something like this w/o adding parens
      .map(_.numBlah)
  }

Answer 1

你可以用 pimp my library 模式模拟它:

  object MyUtils {

    implicit class ListOpts[A](val l: List[A]) extends AnyVal {
      def myMatch[B](pf: PartialFunction[List[A], Option[B]]): Option[B] =
        pf.applyOrElse(l, (_: List[A]) => None)
      }

    ...
  }

然后在范围内导入它

  import MyUtils._

最后，您的无括号管道是

  def foo: Option[Int] = {
    myListOfFoo // imported
      .flatMap(_.barList)
      .filter(_.isGood)
      .toList // Not needed as filter already returns a List
      .myMatch { // resolved implicitly
        case List(bar) => Some(addr)
        case _         => None // Not needed as it's handled by myMatch
      }
      .map(_.getBaz) // would like to do something like this w/o adding parens. Now you can :-)
      .map(_.numBlah)
  }