在Scala 2.10中使用ClassTag / TypeTag代替ClassManifest

Question

I have some code to instantiate a random class like this:

trait T
class A extends T
class B extends T
class C extends T

def createRandomT = {
    val choices = Vector(classOf[A], classOf[B], classOf[C])
    val cls = new scala.util.Random().shuffle(choices).head
    instantiateT(cls)
}                                   

def instantiateT(cls: Class[_ <: T]) = {
    ClassManifest.fromClass(cls) match {
        case c if c <:< classManifest[A] => new A
        case c if c <:< classManifest[B] => new B
        case c if c <:< classManifest[C] => new C
    }
}

This works, but after upgrading to 2.10 instantiateT gives various deprecation warnings.

Any hints how to replicate the functionality with ClassTag and/or TypeTag ?

Edit: As pointed out by Daniel this works:

    cls match {
        case c if c.isAssignableFrom(classOf[A]) => new A
        case c if c.isAssignableFrom(classOf[B]) => new B
        case c if c.isAssignableFrom(classOf[C]) => new C
    }

Answer 1

如果您有一个Class ，则应该只使用isAssignableFrom 。

case c if cls.isAssignableFrom(c.getClass()) => new A

Answer 2

I am not sure why it has to be so complicated... Surely if you already have a Class instance you can just call Class.newInstance ? Like so:

def instantiateT(cls: Class[_ <: T]) = cls.newInstance

Or maybe you are performing a match because in your real code each class has a separate list of (default) argument to pass to the constructor?