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

This is the most complete example how to create case class via reflection with default constructor parameters(Github source):

import scala.reflect.runtime.universe
import scala.reflect.internal.{Definitions, SymbolTable, StdNames}

object Main {
  def newInstanceWithDefaultParameters(className: String): Any = {
    val runtimeMirror: universe.Mirror = universe.runtimeMirror(getClass.getClassLoader)
    val ds = universe.asInstanceOf[Definitions with SymbolTable with StdNames]
    val classSymbol = runtimeMirror.staticClass(className)
    val classMirror = runtimeMirror.reflectClass(classSymbol)
    val moduleSymbol = runtimeMirror.staticModule(className)
    val moduleMirror = runtimeMirror.reflectModule(moduleSymbol)
    val moduleInstanceMirror = runtimeMirror.reflect(moduleMirror.instance)
    val defaultValueMethodSymbols = moduleMirror.symbol.info.members
      .filter(_.name.toString.startsWith(ds.nme.defaultGetterName(ds.newTermName("apply"), 1).toString.dropRight(1)))
      .toSeq
      .reverse
      .map(_.asMethod)
    val defaultValueMethods = defaultValueMethodSymbols.map(moduleInstanceMirror.reflectMethod).toList
    val primaryConstructorMirror = classMirror.reflectConstructor(classSymbol.primaryConstructor.asMethod)
    primaryConstructorMirror.apply(defaultValueMethods.map(_.apply()): _*)
  }

  def main(args: Array[String]): Unit = {
    val instance = newInstanceWithDefaultParameters(classOf[Bar].getName)
    println(instance)
  }
}

case class Bar(i: Int = 33)