scala - Getting subclasses of a sealed trait

Question

Is it possible (via macros, some form of Shapeless automagic or otherwise) to obtain a list of the subclasses of a sealed trait:

• At compile time?
• At runtime?

Answer 1

You don't need any 3rd party library to do this:

sealed trait MyTrait

case object SubClass1 extends MyTrait
case object SubClass2 extends MyTrait

import scala.reflect.runtime.{universe => ru}

val tpe = ru.typeOf[MyTrait]
val clazz = tpe.typeSymbol.asClass
// if you want to ensure the type is a sealed trait, 
// then you can use clazz.isSealed and clazz.isTrait
clazz.knownDirectSubclasses.foreach(println)

Output:

object SubClass1

object SubClass2