Scala example source code file (Reifier.scala)

This example Scala source code file (Reifier.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, cannotreifyerroneousreifee, compiler, javauniverseclass, macro, nosymbol, nsc, reflection, reifiedtype, reifier, reify, throwable, tree, unexpectedreificationexception, valdef

The Reifier.scala Scala example source code

package scala.reflect.reify

import scala.tools.nsc.Global
import scala.reflect.macros.ReificationException
import scala.reflect.macros.UnexpectedReificationException
import scala.reflect.reify.utils.Utils

/** Given a tree or a type, generate a tree that when executed at runtime produces the original tree or type.
 *  See more info in the comments to `reify` in scala.reflect.api.Universe.
 *
 *  @author   Martin Odersky
 *  @version  2.10
 *  @since    2.10
 */
abstract class Reifier extends States
                          with Phases
                          with Errors
                          with Utils {

  val global: Global
  import global._
  import definitions._
  private val runDefinitions = currentRun.runDefinitions
  import runDefinitions._

  val typer: global.analyzer.Typer
  val universe: Tree
  val mirror: Tree
  val reifee: Any
  val concrete: Boolean

  // needed to seamlessly integrate with standalone utils
  override def getReifier: Reifier { val global: Reifier.this.global.type } =
    this.asInstanceOf[Reifier { val global: Reifier.this.global.type }]
  override def hasReifier = true

  /** For `reifee` and other reification parameters, generate a tree of the form
   *  {{{
   *    {
   *      val \$u: universe.type = <[ universe ]>
   *      val \$m: \$u.Mirror = <[ mirror ]>
   *      \$u.Expr[T](rtree)       // if data is a Tree
   *      \$u.TypeTag[T](rtree)    // if data is a Type
   *    }
   *  }}}
   *
   *  where
   *
   *    - `universe` is the tree that represents the universe the result will be bound to.
   *    - `mirror` is the tree that represents the mirror the result will be initially bound to.
   *    - `rtree` is code that generates `reifee` at runtime.
   *    - `T` is the type that corresponds to `data`.
   *
   *  This is not a method, but a value to indicate the fact that Reifier instances are a one-off.
   */
  lazy val reification: Tree = {
    try {
      if (universe exists (_.isErroneous)) CannotReifyErroneousPrefix(universe)
      if (universe.tpe == null) CannotReifyUntypedPrefix(universe)

      val result = reifee match {
        case tree: Tree =>
          reifyTrace("reifying = ")(if (settings.Xshowtrees || settings.XshowtreesCompact || settings.XshowtreesStringified) "\n" + nodePrinters.nodeToString(tree).trim else tree.toString)
          reifyTrace("reifee is located at: ")(tree.pos)
          reifyTrace("universe = ")(universe)
          reifyTrace("mirror = ")(mirror)
          if (tree exists (_.isErroneous)) CannotReifyErroneousReifee(tree)
          if (tree.tpe == null) CannotReifyUntypedReifee(tree)
          val pipeline = mkReificationPipeline
          val rtree = pipeline(tree)

          val tpe = typer.packedType(tree, NoSymbol)
          val ReifiedType(_, _, tpeSymtab, _, rtpe, tpeReificationIsConcrete) = `package`.reifyType(global)(typer, universe, mirror, tpe, concrete = false)
          state.reificationIsConcrete &= tpeReificationIsConcrete
          state.symtab ++= tpeSymtab
          ReifiedTree(universe, mirror, symtab, rtree, tpe, rtpe, reificationIsConcrete)

        case tpe: Type =>
          reifyTrace("reifying = ")(tpe.toString)
          reifyTrace("universe = ")(universe)
          reifyTrace("mirror = ")(mirror)
          val rtree = reify(tpe)
          ReifiedType(universe, mirror, symtab, tpe, rtree, reificationIsConcrete)

        case _ =>
          throw new Error("reifee %s of type %s is not supported".format(reifee, if (reifee == null) "null" else reifee.getClass.toString))
      }

      // todo. why do we reset attrs?
      //
      // typically we do some preprocessing before reification and
      // the code emitted/moved around during preprocessing is very hard to typecheck, so we leave it as it is
      // however this "as it is" sometimes doesn't make any sense
      //
      // ===example 1===
      // we move a freevar from a nested symbol table to a top-level symbol table,
      // and then the reference to $u becomes screwed up, because nested symbol tables are already typechecked,
      // so we have an $u symbol that points to the nested $u rather than to the top-level one.
      //
      // ===example 2===
      // we inline a freevar by replacing a reference to it, e.g. $u.Apply($u.Select($u.Ident($u.newTermName("$u")), $u.newTermName("Ident")), List($u.Ident($u.newTermName("free$x"))))
      // with its original binding (e.g. $u.Ident("x"))
      // we'd love to typecheck the result, but we cannot do this easily, because $u is external to this tree
      // what's even worse, sometimes $u can point to the top-level symbol table's $u, which doesn't have any symbol/type yet -
      // it's just a ValDef that will be emitted only after the reification is completed
      //
      // hence, the simplest solution is to erase all attrs so that invalid (as well as non-existent) bindings get rebound correctly
      // this is ugly, but it's the best we can do
      //
      // todo. this is a common problem with non-trivial macros in our current macro system
      // needs to be solved some day
      // upd. a new hope: https://groups.google.com/forum/#!topic/scala-internals/TtCTPlj_qcQ
      var importantSymbols = Set[Symbol](
        NothingClass, AnyClass, SingletonClass, PredefModule, ScalaRunTimeModule, TypeCreatorClass, TreeCreatorClass, MirrorClass,
        ApiUniverseClass, JavaUniverseClass, ReflectRuntimePackage, runDefinitions.ReflectRuntimeCurrentMirror)
      importantSymbols ++= importantSymbols map (_.companionSymbol)
      importantSymbols ++= importantSymbols map (_.moduleClass)
      importantSymbols ++= importantSymbols map (_.linkedClassOfClass)
      def isImportantSymbol(sym: Symbol): Boolean = sym != null && sym != NoSymbol && importantSymbols(sym)
      val untyped = brutallyResetAttrs(result, leaveAlone = {
        case ValDef(_, u, _, _) if u == nme.UNIVERSE_SHORT => true
        case ValDef(_, m, _, _) if m == nme.MIRROR_SHORT => true
        case tree if symtab.syms contains tree.symbol => true
        case tree if isImportantSymbol(tree.symbol) => true
        case _ => false
      })

      if (reifyCopypaste) {
        if (reifyDebug) println("=============================")
        println(reifiedNodeToString(untyped))
        if (reifyDebug) println("=============================")
      } else {
        reifyTrace("reification = ")(untyped)
      }

      untyped
    } catch {
      case ex: ReificationException =>
        throw ex
      case ex: UnexpectedReificationException =>
        throw ex
      case ex: Throwable =>
        throw new UnexpectedReificationException(defaultErrorPosition, "reification crashed", ex)
    }
  }
}