测试给定实例是否是scala中给定类的(子)类

Question

说你给出的一个实例List[Class[_ <: Base]],并说许多类扩展Base:

class A extends Base
class B extends Base
class C extends A

等等......
现在,给定的列表可能只包含一些类.例如:val classes = classOf[A] :: Nil嗯,如果我val的类是在列表中找到的类型,或者如果它是列表中类的子类,我如何测试实例化？即如何实施:
def testClass(class : List[Class[_ <: Base]], instance : Base) : Boolean
何时:

val classes = classOf[A] :: Nil
testClass(classes, new A) // should return true
testClass(classes, new B) // should return false
testClass(classes, new C) // should return true

用例:
我正在尝试编写一个通用的重试模式,即获取一些非常容易出错的代码,并且我想重试执行一些最大次数的尝试,当每次失败时,它应该执行一些"等待" " 方法.
例如

retryRequest({
    //Some code that throws exceptions
}, classOf[SomeException] :: classOf[SomeOtherException] :: Nil,
100, {Thread.sleep(5000)})

这很好用,但它不会测试给定异常的子类:

def retryRequest(req : => Unit, validExceptions : List[Class[_ <: java.lang.Throwable]], tries : Int, waitMethod : => Unit) {
    var keepTrying = false
    var tryCount = 0
    do{
        try{
            logger.debug("retryRequest, try #" + tryCount)
            keepTrying = false
            req
        }catch{
            case ex if(tryCount >= tries && validExceptions.contains(ex.getClass)) => {
                throw new MaxTriesReachedException("tried for " + tryCount + "times, but no luck. " +
                                                   "you may want to try ommitting generic exceptions types from the given list.") 
            }
            case ex if (validExceptions.contains(ex.getClass)) => {
                logger.debug("intercepted " + ex.toString)
                tryCount += 1
                keepTrying = true
                waitMethod
            }
        }
    }while(keepTrying)
}

我真的想要替换:

validExceptions.contains(ex.getClass)

有类似的东西:

validExceptions.exists(exClass => ex.isInstanceOf[exClass]) //won't compile

可能吗？怎么样？

Answer 1

一种更简单的方法是使用util.control.Exception:

  def retryRequest(req: => Unit, 
                   validExceptions: List[Class[_ <: Throwable]], 
                   tries: Int, 
                   waitMethod: => Unit): Unit =
   (Exception.catching(validExceptions:_*) withApply { e => 
      waitMethod
      if (tries > 1) retryRequest(req, validExceptions, tries - 1, waitMethod)
   }) { req }

  retryRequest( { println("a"); throw new Exception }, 
                List(classOf[Exception]), 
                3,
                Thread.sleep(100))

简而言之:withApply当catching抛出一个传递给异常的异常时,接受一个处理该情况的闭包.在我们的例子中,我们只是递归地称呼自己(假设重试次数很少,我认为这不是问题).

Answer 2

我认为这应该有效:

validExceptions.exists(exClass => exClass.isAssignableFrom(ex.getClass))

http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#isAssignableFrom%28java.lang.Class%29