Scala：抽象类型模式 A 未经检查，因为它被擦除消除了
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Scala: abstract type pattern A is unchecked since it is eliminated by erasure
提问by tmporaries
I am writing the function that can catch exceptions of the certain type only.
我正在编写只能捕获特定类型异常的函数。
def myFunc[A <: Exception]() {
try {
println("Hello world") // or something else
} catch {
case a: A => // warning: abstract type pattern A is unchecked since it is eliminated by erasure
}
}
What is the corrent way to bypass jvm type erasure in such case?
在这种情况下绕过 jvm 类型擦除的正确方法是什么？
回答by senia
You could use ClassTaglike in this answer.
你可以ClassTag在这个答案中使用like 。
But I'd prefer this approach:
但我更喜欢这种方法：
def myFunc(recover: PartialFunction[Throwable, Unit]): Unit = {
try {
println("Hello world") // or something else
} catch {
recover
}
}
Usage:
用法：
myFunc{ case _: MyException => }
Using ClassTag:
使用ClassTag：
import scala.reflect.{ClassTag, classTag}
def myFunc[A <: Exception: ClassTag](): Unit = {
try {
println("Hello world") // or something else
} catch {
case a if classTag[A].runtimeClass.isInstance(a) =>
}
}
Note also that in general you should use Trywith recovermethod: Trywill catch only NonFatalexceptions.
另请注意，通常您应该使用Trywith recovermethod:Try将只捕获NonFatal异常。
def myFunc(recover: PartialFunction[Throwable, Unit]) = {
Try {
println("Hello world") // or something else
} recover {
recover
}.get // you could drop .get here to return `Try[Unit]`
}
回答by Stefan Endrullis
For every type check (e.g. case a: A) the JVM needs the corresponding classobject to perform the check. In your case the JVM does not have the class object, because Ais a variable type parameter. However, you can add additional information about Aby implicitly passing a Manifest[A]to myFunc. As a shorthand you can just add : Manifestto your type declaration of A:
对于每个类型检查（例如case a: A），JVM 需要相应的class对象来执行检查。在您的情况下，JVM 没有类对象，因为A它是变量类型参数。但是，您可以A通过隐式传递 aManifest[A]来添加有关的其他信息myFunc。作为简写，您可以添加: Manifest到您的类型声明中A：
def myFunc[A <: Exception : Manifest]() {
try {
println("Hello world") // or something else
} catch {
case a: A => // warning: abstract type pattern A is unchecked since it is eliminated by erasure
}
}
