How to invoke method on companion object via reflection?

Question

I have a class name and a method whose type parameters I know, and I\'d like to invoke this method via reflection.

In java I\'d do something like:

Cl         


        

Answer 1

The Scala 2.13.3 example coding below invokes a common method apply, in two different cases, by finding the companion object refering to the respective example class:

package spielwiese.reflection_versuche

object Structural_Typing_Companion_Object_Invoke_Testframe {

  // Example 1
  case class Person01(vorname: String, name: String)

  object Person01 {
    def apply(x: Integer): Person01 = new Person01(s"Prename_$x", s"Lastname_$x")
  }

  // Example 2
  case class Person02(vorname: String, name: String)

  object Person02 {
    def apply(x: Integer): Person02 = new Person02(s"Prename_$x", s"Lastname_$x")
  }

  // Invocation demo:

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

  def callGenericCompanionObjectMethod[T](implicit typetag: ru.TypeTag[T]) = {

    val m = ru.runtimeMirror(getClass.getClassLoader)

    val o1 = m.reflectModule(ru.typeOf[T].typeSymbol.companion.asModule).instance

    val o2 = o1.asInstanceOf[{ def apply(x: Integer): T }] // "structural typing"

    o2.apply(123)

  }

  def main(args: Array[String]): Unit = {

    println(callGenericCompanionObjectMethod[Person01]) 
    // prints: "Person01(Prename_123,Lastname_123)"

    println(callGenericCompanionObjectMethod[Person02]) 
    // prints: "Person02(Prename_123,Lastname_123)"

  }

}