Getting constructor arguments out of a case class, printing the names of the args and their runtime values

reflect-extract-ctor-args.scala

import scala.reflect.runtime.universe._

class AbstractParams[T: TypeTag] {
  def tag: TypeTag[T]  = typeTag[T]
  override def toString: String = {
    // Find all case class fields in concrete class instance and print them as "[field name] [field value]"
    val tag = this.tag
    val tpe = tag.tpe
    val allAccessors = tpe.declarations.collect { case meth: MethodSymbol if meth.isCaseAccessor => meth }
    
    val m = runtimeMirror(getClass.getClassLoader)
    val im = m.reflect(this)
    val ctorArg2Strings = allAccessors map { sym =>
      val fldMirror = im.reflectField(sym)
      val value = fldMirror.get
      "[" + sym.name + ": " + value + "]"
    }
    ctorArg2Strings.mkString(" ")
  }
}

case class MyParams(id: String, stuff: Int) extends AbstractParams[MyParams]

object Ex extends App {
  val p = new MyParams("joe", 2)
  println(s"$p")
  // prints:
  // [id: joe] [stuff: 2]
}