Get generic types of child in scala 2.10

Question

class Parent[T: ClassTag] {
}

class Child[U: ClassTag, T: ClassTag] extends Parent[T] {
}

val o: Parent[_] = new Child[Int, String]

Is it possible to get the actual types of T and U given o (note its type Parent[_]), assuming you know o is of type Child?

I have tried a few things based on Runtime resolution of type arguments using scala 2.10 reflection but no luck so far.

Ultimately as strings, for instance in the example given that would be "Int" and "String" — savx2, Jul 24 '15 at 18:17
But how? Is it okay if each class stores the `ClassTag`? Should some method reveal them? Not sure what you intend to use them for. — Michael Zajac, Jul 24 '15 at 18:45

score 0 · Accepted Answer · answered Jul 24 '15 at 20:03

If you modify Parent and Child slightly (note that : ClassTag notation is basically the same except for val, so it doesn't give a name to the implicit parameter or make it accessible from outside the class)

class Parent[T](implicit val tTag: ClassTag[T]) {
}

class Child[U, T](implicit override val tTag: ClassTag[T], val uTag: ClassTag[U]) extends Parent[T] {
}

then you can do

val tTag = o.tTag // ClassTag[String]

Of course, if you need uTag, you'll have to cast: o.asInstanceOf[Child[_, _]].uTag, but it'll work

assuming you know o is of type Child

Get generic types of child in scala 2.10

1 Answers1