How to capture T from TypeTag[T] or any other generic in scala?

Question

Found how to obtain typeTag for least common supertype. But how to capture typetag\'s generic into type alias to operate type itself?

Assuming TypeTag[SomeType

Answer 1

This will work if typeTag's generic was not erased (enough for extracting common supertype of types, that are known at compilation time):

class TypeHolder { type T }
object TypeHolder {
  def apply[U](a: TypeTag[U]) = new TypeHolder{type T = U} 
}

Usage:

val typ = TypeHolder(typeTag[Int])
val k: typ.T = 5
val list = List[typ.T]()
trait A { def aaaa: typ.T } 
someObject.isInstanceOf[typ.T]

But you can't do it with type variable because it will be "erased" to Any