scala 中的匹配类型

发布于 2024-10-23 22:07:25 字数 315 浏览 1 评论 0原文

Scala 中可以匹配类型吗？像这样的东西：（

  def apply[T] = T match {
    case String => "you gave me a String",
    case Array  => "you gave me an Array"
    case _ => "I don't know what type that is!"
  }

但是显然可以编译:)）

或者也许正确的方法是类型重载......这可能吗？

不幸的是，我无法向它传递对象的实例和模式匹配。

原文

Is it possible to match types in Scala? Something like this:

  def apply[T] = T match {
    case String => "you gave me a String",
    case Array  => "you gave me an Array"
    case _ => "I don't know what type that is!"
  }

(But that compiles, obviously :))

Or perhaps the right approach is type overloading…is that possible?

I cannot pass it an instance of an object and pattern match on that, unfortunately.

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み青杉依旧 2024-10-30 22:07:25

def apply[T](t: T) = t match {
  case _: String => "you gave me a String"
  case _: Array[_]  => "you gave me an Array"
  case _ => "I don't know what type that is!"
}

def apply[T](t: T) = t match {
  case _: String => "you gave me a String"
  case _: Array[_]  => "you gave me an Array"
  case _ => "I don't know what type that is!"
}

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荒芜了季节 2024-10-30 22:07:25

您可以使用清单并对其进行模式匹配。不过，传递数组类的情况是有问题的，因为 JVM 对每种数组类型使用不同的类。要解决此问题，您可以检查有问题的类型是否已删除到数组类中：

val StringManifest = manifest[String]

def apply[T : Manifest] = manifest[T] match {
  case StringManifest => "you gave me a String"
  case x if x.erasure.isArray => "you gave me an Array"
  case _ => "I don't know what type that is!"
}

You can use manifests and do a pattern match on them. The case when passing an array class is problematic though, as the JVM uses a different class for each array type. To work around this issue you can check if the type in question is erased to an array class:

val StringManifest = manifest[String]

def apply[T : Manifest] = manifest[T] match {
  case StringManifest => "you gave me a String"
  case x if x.erasure.isArray => "you gave me an Array"
  case _ => "I don't know what type that is!"
}

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水溶 2024-10-30 22:07:25

Manifest id 已弃用。但您可以使用 TypeTag

import scala.reflect.runtime.universe._

def fn[R](r: R)(implicit tag: TypeTag[R]) {

  typeOf(tag) match {
       case t if t =:= typeOf[String] => "you gave me a String"
       case t if t =:= typeOf[Array[_]] => "you gave me an Array"
       case _ => "I don't know what type that is!"
  }
}

希望这会有所帮助。

Manifest id deprecated. But you can use TypeTag

import scala.reflect.runtime.universe._

def fn[R](r: R)(implicit tag: TypeTag[R]) {

  typeOf(tag) match {
       case t if t =:= typeOf[String] => "you gave me a String"
       case t if t =:= typeOf[Array[_]] => "you gave me an Array"
       case _ => "I don't know what type that is!"
  }
}

Hope this helps.

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