Instantiating a case class with default args via reflection

Question

I need to be able to instantiate various case classes through reflection, both by figuring out the argument types of the constructor, as well as invoking the constructor with al

Answer 1

So in the linked question, the :power REPL uses internal API, which means that defaultGetterName is not available, so we need to construct that from hand. An adoption from @som-snytt 's answer:

def newDefault[A](implicit t: reflect.ClassTag[A]): A = {
  import reflect.runtime.{universe => ru, currentMirror => cm}

  val clazz  = cm.classSymbol(t.runtimeClass)
  val mod    = clazz.companionSymbol.asModule
  val im     = cm.reflect(cm.reflectModule(mod).instance)
  val ts     = im.symbol.typeSignature
  val mApply = ts.member(ru.newTermName("apply")).asMethod
  val syms   = mApply.paramss.flatten
  val args   = syms.zipWithIndex.map { case (p, i) =>
    val mDef = ts.member(ru.newTermName(s"apply$$default$$${i+1}")).asMethod
    im.reflectMethod(mDef)()
  }
  im.reflectMethod(mApply)(args: _*).asInstanceOf[A]
}

case class Foo(bar: Int = 33)

val f = newDefault[Foo]  // ok

Is this really the shortest path?