Scala trait runtime class from type parameter

scala, type-parameter

Solution

Nice and common way of working around type erasure in Scala is to use `ClassTag`s. They're usually passed as implicit parameters. Unfortunately, traits can't take constructor parameters, so the best that we can have is:

import scala.reflect.ClassTag

trait MyTrait[T <: Enum] {
  val ttag: ClassTag[T]

  def myMethod(name: String): T = {
    MyJavaClass.staticMethod(name, ttag.runtimeClass.asInstanceOf[Class[T]])
  }
}

Then, every class extending `MyTrait` must be defined like this:

class MyClass[T <: Enum](/*your params, if any*/)(implicit val ttag: ClassTag[T]) extends MyTrait[T] {
  /*your class body*/
}

Then, if you have some concrete enum `MyEnum`, you can create instances of your class seamlessly:

new MyClass[MyEnum](/*your params, if any*/)

Problem

I have a scala trait [this trait does not compile] ``` trait MyTrait[T <: Enum] { def myMethod(name: String): T = { MyJavaClass.staticMethod(name, classOf[T]) } } ``` And a Java class ``` public class MyJavaClass { public static <T extends Enum> T staticMethod(String name, Class<T> c) { return (T) T.valueOf(c, name); } } ``` How can I make the trait valid scala? What I'm currently doing is adding a `Class[T]` field like this ``` trait MyTrait[T <: Enum] { val t: Class[T] def myMethod(name: String): T = { MyJavaClass.staticMethod(name, t) } } ``` but I don't like having to add a `t` field to all classes that want to use this trait.

Original source