匹配 Java 接口(interface)时的 Scala match/case 语句

Question

我正在使用 Scala match/case用于匹配给定 java 类的接口(interface)的语句。我希望能够检查一个类是否实现了接口(interface)的组合。我似乎可以让它工作的唯一方法是使用嵌套 match/case看起来丑陋的陈述。

假设我有一个实现 Person、Manager 和 Investor 的 PersonImpl 对象。我想看看 PersonImpl 是否同时实现了 Manager 和 Investor。我应该能够做到以下几点:

person match {
  case person: (Manager, Investor) =>
    // do something, the person is both a manager and an investor
  case person: Manager =>
    // do something, the person is only a manager
  case person: Investor =>
    // do something, the person is only an investor
  case _ =>
    // person is neither, error out.
}

case person: (Manager, Investor)只是行不通。为了让它工作，我必须做以下看起来很难看的事情。

person match {
  case person: Manager = {
    person match {
      case person: Investor =>
        // do something, the person is both a manager and investor
      case _ =>
        // do something, the person is only a manager
    }
  case person: Investor =>
    // do something, the person is only an investor.
  case _ =>
    // person is neither, error out.
}

这简直丑陋。有什么建议么？

Answer 1

试试这个:

case person: Manager with Investor => // ...

with用于您可能想要表达类型交集的其他场景，例如在类型绑定(bind)中:

def processGenericManagerInvestor[T <: Manager with Investor](person: T): T  = // ...

顺便说一句—— 并不是说这是推荐的做法 , 但是——你也可以这样测试它: if (person.isInstanceOf[Manager] && person.isInstanceOf[Investor]) ... .

编辑:这对我很有效:

trait A
trait B
class C

def printInfo(a: Any) = println(a match {
  case _: A with B => "A with B"
  case _: A => "A"
  case _: B => "B"
  case _ => "unknown"
})

def main(args: Array[String]) {
  printInfo(new C)               // prints unknown
  printInfo(new C with A)        // prints A
  printInfo(new C with B)        // prints B
  printInfo(new C with A with B) // prints A with B
  printInfo(new C with B with A) // prints A with B
}