在Scala中匹配類型

Question

是否可以在Scala中匹配類型？ 像這樣：

  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!"
  }

（但是編譯，很明顯:)）

也許正確的方法是類型重載……可能嗎？

不幸的是，我無法將其傳遞給對象和模式匹配的實例。

Answer 1

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!"
}

Answer 2

您可以使用清單並對其進行模式匹配。 但是，傳遞數組類的情況是有問題的，因為JVM對每種數組類型使用不同的類。 要變通解決此問題，您可以檢查是否有問題的類型被擦除為數組類：

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!"
}

Answer 3

Manifest ID已棄用。 但是你可以使用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!"
  }
}

希望這可以幫助。