sealed subclass copier

sealed-subclass-copier.scala

scala> object O {
     |   sealed abstract class Base;
     |   case class Foo(id: Int, b: String) extends Base
     |   case class Bar(id: Int, b: Boolean) extends Base
     | }
defined module O

scala> import O._
import O._

scala>

scala> val cm = scala.reflect.runtime.currentMirror
cm: reflect.runtime.universe.Mirror = JavaMirror with scala.tools.nsc.interpreter.IMain$TranslatingClassLoader@4eb63dfe of type class scala.tools.nsc.interpreter.IMain$TranslatingClassLoader with classpath [(memory)] and parent being scala.tools.nsc.util.ScalaClassLoader$URLClassLoader@1ea01711 of type class scala.tools.nsc.util.ScalaClassLoader$URLClassLoader with classpath [file:/Library/Java/JavaVirtualMachines/1.6.0_37-b06-434.jdk/Contents/Classes/classes.jar,file:/Library/Java/JavaVirtualMachines/1.6.0_37-b06-434.jdk/Contents/Classes/ui.jar,file:/Library/Java/JavaVirtualMachines/1.6.0_37-b06-434.jdk/Contents/Classes/jsse.jar,file:/Library/Java/JavaVirtualMachines/1.6.0_37-b06-434.jdk/Contents/Classes/jce.jar,file:/Library/Java/JavaVirtualMachines/1.6.0_37-b06-434.jdk/Contents/Class...
scala> import cm.universe._
import cm.universe._

scala>

scala> val function: Function = {
     |   val base = typeOf[Base].typeSymbol.asClass
     |   val subs = base.knownDirectSubclasses.toList
     |
     |   object copierNme {
     |     val x: TermName     = "x"
     |     val base: TermName  = "base"
     |     val id: TermName    = "id"
     |     val newId: TermName = "newId"
     |     val copy: TermName  = "copy"
     |   }
     |   def mkCase(subClass: Symbol) = {
     |     val bind = Bind(copierNme.x, Typed(Ident(nme.WILDCARD), Ident(subClass)))
     |     val copyApply = Apply(Select(Ident(copierNme.x), copierNme.copy), List(AssignOrNamedArg(Ident(copierNme.id), Ident(copierNme.newId))))
     |     CaseDef(bind, EmptyTree, copyApply)
     |   }
     |   val param1 = ValDef(Modifiers(Flag.PARAM), copierNme.base, TypeTree(typeOf[Base]), EmptyTree)
     |   val param2 = ValDef(Modifiers(Flag.PARAM), copierNme.newId, TypeTree(typeOf[Int]), EmptyTree)
     |   Function(List(param1, param2), Match(Ident(copierNme.base), subs map mkCase))
     | }
function: cm.universe.Function =
((base: O.Base, newId: Int) => base match {
  case (x @ (_: Bar)) => x.copy(id = newId)
  case (x @ (_: Foo)) => x.copy(id = newId)
})

scala>

scala> import scala.tools.reflect.ToolBox
import scala.tools.reflect.ToolBox

scala> val tb = cm.mkToolBox()
tb: scala.tools.reflect.ToolBox[reflect.runtime.universe.type] = scala.tools.reflect.ToolBoxFactory$ToolBoxImpl@60b705e9

scala> val idCopier = tb.compile(function)().asInstanceOf[((Base, Int) => Base)]
idCopier: (O.Base, Int) => O.Base = <function2>

scala>

scala> idCopier(Foo(0, "a"), 1)  // Foo(1,a)
res30: O.Base = Foo(1,a)

scala> idCopier(Bar(0, true), 2) // Bar(1, true)
res31: O.Base = Bar(2,true)