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Scala example source code file (Mirrors.scala)

This example Scala source code file (Mirrors.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; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

classsymbol, emptypackage, emptypackageclass, modulesymbol, name, nosymbol, rootclass, rootpackage, string, symbol

The Mirrors.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky

package scala
package reflect
package internal

import Flags._

trait Mirrors extends api.Mirrors {
  thisUniverse: SymbolTable =>

  override type Mirror >: Null <: RootsBase

  // root symbols hold a strong reference to the enclosing mirror
  // this prevents the mirror from being collected
  // if there are any symbols created by that mirror
  trait RootSymbol extends Symbol { def mirror: Mirror }

  abstract class RootsBase(rootOwner: Symbol) extends scala.reflect.api.Mirror[Mirrors.this.type] { thisMirror =>
    private[this] var initialized = false
    def isMirrorInitialized = initialized

    protected[scala] def rootLoader: LazyType

    val RootClass: ClassSymbol
    val RootPackage: ModuleSymbol
    val EmptyPackageClass: ClassSymbol
    val EmptyPackage: ModuleSymbol

    def symbolOf[T: universe.WeakTypeTag]: universe.TypeSymbol = universe.weakTypeTag[T].in(this).tpe.typeSymbolDirect.asType

    def findMemberFromRoot(fullName: Name): Symbol = {
      val segs = nme.segments(fullName.toString, fullName.isTermName)
      if (segs.isEmpty) NoSymbol
      else definitions.findNamedMember(segs.tail, member segs.head)

    /** Todo: organize similar to mkStatic in scala.reflect.Base */
    private def getModuleOrClass(path: Name, len: Int): Symbol = {
      val point = path lastPos('.', len - 1)
      val owner =
        if (point > 0) getModuleOrClass(path.toTermName, point)
        else RootClass
      val name = path subName (point + 1, len)
      val sym = member name
      val result = if (path.isTermName) sym.suchThat(_ hasFlag MODULE) else sym
      if (result != NoSymbol) result
      else {
        if (settings.debug) { log(; log( }//debug
        thisMirror.missingHook(owner, name) orElse {
          MissingRequirementError.notFound((if (path.isTermName) "object " else "class ")+path+" in "+thisMirror)

    /** If you're looking for a class, pass a type name.
     *  If a module, a term name.
     *  Unlike `getModuleOrClass`, this function
     *  loads unqualified names from the root package.
    private def getModuleOrClass(path: Name): Symbol =
      getModuleOrClass(path, path.length)

    /** If you're looking for a class, pass a type name.
     *  If a module, a term name.
     *  Unlike `getModuleOrClass`, this function
     *  loads unqualified names from the empty package.
    private def staticModuleOrClass(path: Name): Symbol = {
      val isPackageless = path.pos('.') == path.length
      if (isPackageless) decl path
      else getModuleOrClass(path)

    protected def mirrorMissingHook(owner: Symbol, name: Name): Symbol = NoSymbol

    protected def universeMissingHook(owner: Symbol, name: Name): Symbol = thisUniverse.missingHook(owner, name)

    private[scala] def missingHook(owner: Symbol, name: Name): Symbol = logResult(s"missingHook($owner, $name)")(
      mirrorMissingHook(owner, name) orElse universeMissingHook(owner, name)

    // todo: get rid of most the methods here and keep just staticClass/Module/Package

    /************************ loaders of class symbols ************************/

    private def ensureClassSymbol(fullname: String, sym: Symbol): ClassSymbol = {
      var result = sym
      while (result.isAliasType) result =
      result match {
        case x: ClassSymbol => x
        case _              => MissingRequirementError.notFound("class " + fullname)

    def getClassByName(fullname: Name): ClassSymbol =
      ensureClassSymbol(fullname.toString, getModuleOrClass(fullname.toTypeName))

    def getRequiredClass(fullname: String): ClassSymbol =

    def requiredClass[T: ClassTag] : ClassSymbol =

    def getClassIfDefined(fullname: String): Symbol =

    def getClassIfDefined(fullname: Name): Symbol =

    /** @inheritdoc
     *  Unlike getClassByName/getRequiredClass this function can also load packageless symbols.
     *  Compiler might ignore them, but they should be loadable with macros.
    override def staticClass(fullname: String): ClassSymbol =
      try ensureClassSymbol(fullname, staticModuleOrClass(newTypeNameCached(fullname)))
      catch { case mre: MissingRequirementError => throw new ScalaReflectionException(mre.msg) }

    /************************ loaders of module symbols ************************/

    private def ensureModuleSymbol(fullname: String, sym: Symbol, allowPackages: Boolean): ModuleSymbol =
      sym match {
        case x: ModuleSymbol if allowPackages || !x.hasPackageFlag => x
        case _                                                     => MissingRequirementError.notFound("object " + fullname)

    def getModuleByName(fullname: Name): ModuleSymbol =
      ensureModuleSymbol(fullname.toString, getModuleOrClass(fullname.toTermName), allowPackages = true)

    def getRequiredModule(fullname: String): ModuleSymbol =

    // TODO: What syntax do we think should work here? Say you have an object
    // like scala.Predef.  You can't say requiredModule[scala.Predef] since there's
    // no accompanying Predef class, and if you say requiredModule[scala.Predef.type]
    // the name found via the erasure is scala.Predef$.  For now I am
    // removing the trailing $, but I think that classTag should have
    // a method which returns a usable name, one which doesn't expose this
    // detail of the backend.
    def requiredModule[T: ClassTag] : ModuleSymbol =
      getRequiredModule(erasureName[T] stripSuffix "$")

    def getModuleIfDefined(fullname: String): Symbol =

    def getModuleIfDefined(fullname: Name): Symbol =

    /** @inheritdoc
     *  Unlike getModule/getRequiredModule this function can also load packageless symbols.
     *  Compiler might ignore them, but they should be loadable with macros.
    override def staticModule(fullname: String): ModuleSymbol =
      try ensureModuleSymbol(fullname, staticModuleOrClass(newTermNameCached(fullname)), allowPackages = false)
      catch { case mre: MissingRequirementError => throw new ScalaReflectionException(mre.msg) }

    /************************ loaders of package symbols ************************/

    private def ensurePackageSymbol(fullname: String, sym: Symbol, allowModules: Boolean): ModuleSymbol =
      sym match {
        case x: ModuleSymbol if allowModules || x.hasPackageFlag => x
        case _                                                   => MissingRequirementError.notFound("package " + fullname)

    def getPackage(fullname: TermName): ModuleSymbol =
      ensurePackageSymbol(fullname.toString, getModuleOrClass(fullname), allowModules = true)

    def getPackageIfDefined(fullname: TermName): Symbol =

    @deprecated("Use getPackage", "2.11.0") def getRequiredPackage(fullname: String): ModuleSymbol =

    def getPackageObject(fullname: String): ModuleSymbol = getPackageObject(newTermName(fullname))
    def getPackageObject(fullname: TermName): ModuleSymbol =
      (getPackage(fullname).info member nme.PACKAGE) match {
        case x: ModuleSymbol => x
        case _               => MissingRequirementError.notFound("package object " + fullname)

    def getPackageObjectIfDefined(fullname: String): Symbol =

    def getPackageObjectIfDefined(fullname: TermName): Symbol =

    final def getPackageObjectWithMember(pre: Type, sym: Symbol): Symbol = {
      // The owner of a symbol which requires package qualification may be the
      // package object iself, but it also could be any superclass of the package
      // object.  In the latter case, we must go through the qualifier's info
      // to obtain the right symbol.
      if (sym.owner.isModuleClass) sym.owner.sourceModule // fast path, if the member is owned by a module class, that must be linked to the package object
      else pre member nme.PACKAGE                         // otherwise we have to findMember

    override def staticPackage(fullname: String): ModuleSymbol =
      try ensurePackageSymbol(fullname.toString, getModuleOrClass(newTermNameCached(fullname)), allowModules = false)
      catch { case mre: MissingRequirementError => throw new ScalaReflectionException(mre.msg) }

    /************************ helpers ************************/

    def erasureName[T: ClassTag] : String = {
      /* We'd like the String representation to be a valid
       * scala type, so we have to decode the jvm's secret language.
      def erasureString(clazz: Class[_]): String = {
        if (clazz.isArray) "Array[" + erasureString(clazz.getComponentType) + "]"
        else clazz.getName

   @inline final def wrapMissing(body: => Symbol): Symbol =
      try body
      catch { case _: MissingRequirementError => NoSymbol }

    /** getModule2/getClass2 aren't needed at present but may be again,
     *  so for now they're mothballed.
    // def getModule2(name1: Name, name2: Name) = {
    //   try getModuleOrClass(name1.toTermName)
    //   catch { case ex1: FatalError =>
    //     try getModuleOrClass(name2.toTermName)
    //     catch { case ex2: FatalError => throw ex1 }
    //   }
    // }
    // def getClass2(name1: Name, name2: Name) = {
    //   try {
    //     val result = getModuleOrClass(name1.toTypeName)
    //     if (result.isAliasType) getClass(name2) else result
    //   }
    //   catch { case ex1: FatalError =>
    //     try getModuleOrClass(name2.toTypeName)
    //     catch { case ex2: FatalError => throw ex1 }
    //   }
    // }

    def init() {
      if (initialized) return
      // Still fiddling with whether it's cleaner to do some of this setup here
      // or from constructors.  The latter approach tends to invite init order issues.

      EmptyPackageClass setInfo rootLoader
      EmptyPackage setInfo EmptyPackageClass.tpe

      connectModuleToClass(EmptyPackage, EmptyPackageClass)
      connectModuleToClass(RootPackage, RootClass) enter EmptyPackage enter RootPackage

      if (rootOwner != NoSymbol) {
        // synthetic core classes are only present in root mirrors
        // because Definitions.scala, which initializes and enters them, only affects rootMirror
        // therefore we need to enter them manually for non-root mirrors
        definitions.syntheticCoreClasses foreach (theirSym => {
          val theirOwner = theirSym.owner
          assert(theirOwner.isPackageClass, s"theirSym = $theirSym, theirOwner = $theirOwner")
          val ourOwner = staticPackage(theirOwner.fullName).moduleClass
          val ourSym = theirSym // just copy the symbol into our branch of the symbol table
 enterIfNew ourSym

      initialized = true

  abstract class Roots(rootOwner: Symbol) extends RootsBase(rootOwner) { thisMirror =>

    // TODO - having these as objects means they elude the attempt to
    // add synchronization in SynchronizedSymbols.  But we should either
    // flip on object overrides or find some other accomodation, because
    // lazy vals are unnecessarily expensive relative to objects and it
    // is very beneficial for a handful of bootstrap symbols to have
    // first class identities
    sealed trait WellKnownSymbol extends Symbol {
      this initFlags (TopLevelCreationFlags | STATIC)
    // Features common to RootClass and RootPackage, the roots of all
    // type and term symbols respectively.
    sealed trait RootSymbol extends WellKnownSymbol with thisUniverse.RootSymbol {
      final override def isRootSymbol = true
      override def owner              = rootOwner
      override def typeOfThis         = thisSym.tpe
      def mirror                      = thisMirror.asInstanceOf[Mirror]

    class RootPackage extends ModuleSymbol(rootOwner, NoPosition, nme.ROOTPKG) with RootSymbol {
      this setInfo NullaryMethodType(RootClass.tpe)

      override def isRootPackage = true

    // This is the package _root_.  The actual root cannot be referenced at
    // the source level, but _root_ is essentially a function => <root>.
    lazy val RootPackage = new RootPackage

    class RootClass extends PackageClassSymbol(rootOwner, NoPosition, tpnme.ROOT) with RootSymbol {
      this setInfo rootLoader

      override def isRoot            = true
      override def isEffectiveRoot   = true
      override def isNestedClass     = false
      override def sourceModule      = RootPackage

    // This is <root>, the actual root of everything except the package _root_.
    // <root> and _root_ (RootPackage and RootClass) should be the only "well known"
    // symbols owned by NoSymbol.  All owner chains should go through RootClass,
    // although it is probable that some symbols are created as direct children
    // of NoSymbol to ensure they will not be stumbled upon.  (We should designate
    // a better encapsulated place for that.)
    lazy val RootClass = new RootClass

    class EmptyPackage extends ModuleSymbol(RootClass, NoPosition, nme.EMPTY_PACKAGE_NAME) with WellKnownSymbol {
      override def isEmptyPackage = true

    // The empty package, which holds all top level types without given packages.
    lazy val EmptyPackage = new EmptyPackage

    class EmptyPackageClass extends PackageClassSymbol(RootClass, NoPosition, tpnme.EMPTY_PACKAGE_NAME) with WellKnownSymbol {
      override def isEffectiveRoot     = true
      override def isEmptyPackageClass = true
      override def sourceModule        = EmptyPackage

    lazy val EmptyPackageClass = new EmptyPackageClass

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