是否可以
编写一个泛型函数,该函数接受类型为"Any"的值,泛型类型参数为"T",并通过检查传入值的运行时类型返回 Option[T]?
我尝试了 repl (Scala 版本 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_66))
def cast[T](x: Any): Option[T] = x match {
case v: T => Some(v)
case _ => Option.empty[T]
}
我收到警告:
warning: abstract type pattern T is unchecked since it is eliminated by erasure
case v: T => Some(v)
我如何传入类类型并进行显式类型检查而不是泛型?
附言显然是由于类型擦除,上面的代码爆炸了。示例 repl 交互:
scala> val x :Any = 123
x: Any = 123
scala> cast[Int](x)
res0: Option[Int] = Some(123)
scala> cast[String](x)
res1: Option[String] = Some(123)
scala> val x :Any = "dfg"
x: Any = dfg
scala> cast[Int](x)
res2: Option[Int] = Some(dfg)
scala> cast[Int](x).get
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
at scala.runtime.BoxesRunTime.unboxToInt(BoxesRunTime.java:101)
... 33 elided
您需要
为运行时类型提供一个ClassTag
:
def cast[T: ClassTag](x: Any): Option[T] = x match {
case v: T => Some(v)
case _ => Option.empty[T]
}
println(cast[Int](1))
println(cast[Int]("hello"))
收益 率:
Some(1)
None