CODEWITHSUNDEEP
scalascala-2.10
hezamu
hezamu

Reputation: 1584

Using ClassTag/TypeTag instead of ClassManifest in Scala 2.10

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
    }

Upvotes: 2

Views: 1255

Answers (2)

R&#233;gis Jean-Gilles
R&#233;gis Jean-Gilles

Reputation: 32719

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?

Upvotes: 2

Daniel C. Sobral
Daniel C. Sobral

Reputation: 297195

If you've got a Class, you should just use isAssignableFrom.

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

Upvotes: 2

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