Scala 多类型模式匹配
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Scala multiple type pattern matching
提问by psisoyev
I'm wondering how can I use multiple type pattern matching. I have:
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()
}
So I'd like to write something like:
所以我想写一些类似的东西：
x match {
case a @ (MyFirst | MySecond) => doSomething()
case _ => doSomethingElse()
}
I saw similar construction in some tutorial, but it gives me error:
我在一些教程中看到了类似的结构，但它给了我错误：
pattern type is incompatible with expected type;
[error] found : object MyFirst
[error] required: MyAbstract
So is there a way to define few different types in on case clause? I think it would make code prettier. As if I will have 5 of them, I will write same code 5 times (calling doSomething()).
那么有没有办法在 on case 子句中定义几种不同的类型？我认为这会使代码更漂亮。好像我将有 5 个，我将编写相同的代码 5 次（调用 doSomething()）。
Thanks in advance!
提前致谢！
回答by Faiz
You are missing the parenthesis for your case classes. Case classes without parameter lists are deprecated.
您缺少案例类的括号。不推荐使用没有参数列表的案例类。
Try this:
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()
}
If you have too many params for your case classes and don't like having to write long Foo(_,_,..)patterns, then maybe:
如果您的案例类有太多参数并且不想编写长Foo(_,_,..)模式，那么可能：
x match {
case aOrB @ (_:MyFirst | _:MySecond) => doSomething(aOrB)
case _ => doSomethingElse()
}
Or just:
要不就：
x match {
case _:MyFirst | _:MySecond => doSomething(x) // just use x instead of aOrB
case _ => doSomethingElse(x)
}
But perhaps you just wanted singleton case objects?
但也许你只是想要单例 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()
}
