Scala多类型模式匹配

bsxbgnwa 于 2022-12-23 发布在 Scala

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我想知道如何使用多类型模式匹配。我有：

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()
}

所以我想这样写：

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

我在一些教程中看到过类似的构造，但它给了我错误：

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

那么有没有一种方法可以在on case子句中定义更少的类型呢？我认为这会让代码更漂亮。如果我有5个类型，我会写5次相同的代码（调用doSomething（））。

scala

来源：https://stackoverflow.com/questions/15655817/scala-multiple-type-pattern-matching

1条答案

按热度按时间

rryofs0p1#

事例类缺少括号。不推荐使用不带参数列表的事例类。
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()
}

如果你的case类有太多的参数，并且不喜欢写长的Foo(_,_,..)模式，那么也许：

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

或者只是：

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

但也许您只是想要单例case对象？

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()
}

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Scala多类型模式匹配

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