多类型模式匹配

Question

abstract class MyAbstract

case class MyFirst extends MyAbstract
case class MySecond extends MyAbstract
case class MyThird extends MyAbstract // shouldn't be matched and shouldn't call doSomething()

val x: MyAbstract = MyFirst

x match { 
 case a: MyFirst => doSomething()
 case b: MySecond => doSomething()
 case _ => doSomethingElse()
}

x match {
 case a @ (MyFirst | MySecond) => doSomething()
 case _ => doSomethingElse()
}

pattern type is incompatible with expected type;
[error]  found   : object MyFirst
[error]  required: MyAbstract

Answer 1

缺少case类的括号。不推荐使用没有参数列表的Case类。

试试这个：

abstract class MyAbstract
case class MyFirst() extends MyAbstract
case class MySecond() extends MyAbstract

val x: MyAbstract = MyFirst()


x match {
   case aOrB @ (MyFirst() | MySecond()) => doSomething(aOrB)
   case _ => doSomethingElse()
}

如果您的case类有太多的param，并且不喜欢编写长foo(_,_,..)模式，那么可能：

x match {
   case aOrB @ (_:MyFirst | _:MySecond) => doSomething(aOrB)
   case _ => doSomethingElse()
}

x match {
   case _:MyFirst | _:MySecond => doSomething(x) // just use x instead of aOrB
   case _ => doSomethingElse(x)
}

abstract class MyAbstract
case object MyFirst extends MyAbstract
case object MySecond extends MyAbstract

val x: MyAbstract = MyFirst

x match {
   case aOrB @ (MyFirst | MySecond) => doSomething()
   case _ => doSomethingElse()
}