Scala example source code file (MemberHandlers.scala)

This example Scala source code file (MemberHandlers.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

collection, compiler, defdef, importvarstraverser, list, memberdefhandler, memberhandler, name, nsc, option, request, string, tree

The MemberHandlers.scala Scala example source code

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

package scala.tools.nsc
package interpreter

import scala.collection.{ mutable, immutable }
import scala.language.implicitConversions

trait MemberHandlers {
  val intp: IMain

  import intp.{ Request, global, naming }
  import global._
  import naming._

  private def codegenln(leadingPlus: Boolean, xs: String*): String = codegen(leadingPlus, (xs ++ Array("\n")): _*)
  private def codegenln(xs: String*): String = codegenln(true, xs: _*)
  private def codegen(leadingPlus: Boolean, xs: String*): String = {
    val front = if (leadingPlus) "+ " else ""
    front + (xs map string2codeQuoted mkString " + ")
  }
  private implicit def name2string(name: Name) = name.toString

  /** A traverser that finds all mentioned identifiers, i.e. things
   *  that need to be imported.  It might return extra names.
   */
  private class ImportVarsTraverser extends Traverser {
    val importVars = new mutable.HashSet[Name]()

    override def traverse(ast: Tree) = ast match {
      case Ident(name) =>
        // XXX this is obviously inadequate but it's going to require some effort
        // to get right.
        if (name.toString startsWith "x$") ()
        else importVars += name
      case _        => super.traverse(ast)
    }
  }
  private object ImportVarsTraverser {
    def apply(member: Tree) = {
      val ivt = new ImportVarsTraverser()
      ivt traverse member
      ivt.importVars.toList
    }
  }

  private def isTermMacro(ddef: DefDef): Boolean = ddef.mods.isMacro

  def chooseHandler(member: Tree): MemberHandler = member match {
    case member: DefDef if isTermMacro(member) => new TermMacroHandler(member)
    case member: DefDef                        => new DefHandler(member)
    case member: ValDef                        => new ValHandler(member)
    case member: ModuleDef                     => new ModuleHandler(member)
    case member: ClassDef                      => new ClassHandler(member)
    case member: TypeDef                       => new TypeAliasHandler(member)
    case member: Assign                        => new AssignHandler(member)
    case member: Import                        => new ImportHandler(member)
    case DocDef(_, documented)                 => chooseHandler(documented)
    case member                                => new GenericHandler(member)
  }

  sealed abstract class MemberDefHandler(override val member: MemberDef) extends MemberHandler(member) {
    override def name: Name = member.name
    def mods: Modifiers     = member.mods
    def keyword             = member.keyword
    def prettyName          = name.decode

    override def definesImplicit = member.mods.isImplicit
    override def definesTerm: Option[TermName] = Some(name.toTermName) filter (_ => name.isTermName)
    override def definesType: Option[TypeName] = Some(name.toTypeName) filter (_ => name.isTypeName)
    override def definedSymbols = if (symbol.exists) symbol :: Nil else Nil
  }

  /** Class to handle one member among all the members included
   *  in a single interpreter request.
   */
  sealed abstract class MemberHandler(val member: Tree) {
    def name: Name      = nme.NO_NAME
    def path            = intp.originalPath(symbol)
    def symbol          = if (member.symbol eq null) NoSymbol else member.symbol
    def definesImplicit = false
    def definesValue    = false

    def definesTerm     = Option.empty[TermName]
    def definesType     = Option.empty[TypeName]

    private lazy val _referencedNames = ImportVarsTraverser(member)
    def referencedNames = _referencedNames
    def importedNames   = List[Name]()
    def definedNames    = definesTerm.toList ++ definesType.toList
    def definedSymbols  = List[Symbol]()

    def extraCodeToEvaluate(req: Request): String = ""
    def resultExtractionCode(req: Request): String = ""

    private def shortName = this.getClass.toString split '.' last
    override def toString = shortName + referencedNames.mkString(" (refs: ", ", ", ")")
  }

  class GenericHandler(member: Tree) extends MemberHandler(member)

  class ValHandler(member: ValDef) extends MemberDefHandler(member) {
    val maxStringElements = 1000  // no need to mkString billions of elements
    override def definesValue = true

    override def resultExtractionCode(req: Request): String = {
      val isInternal = isUserVarName(name) && req.lookupTypeOf(name) == "Unit"
      if (!mods.isPublic || isInternal) ""
      else {
        // if this is a lazy val we avoid evaluating it here
        val resultString =
          if (mods.isLazy) codegenln(false, "<lazy>")
          else any2stringOf(path, maxStringElements)

        val vidString =
          if (replProps.vids) s"""" + " @ " + "%%8x".format(System.identityHashCode($path)) + " """.trim
          else ""

        """ + "%s%s: %s = " + %s""".format(string2code(prettyName), vidString, string2code(req typeOf name), resultString)
      }
    }
  }

  class DefHandler(member: DefDef) extends MemberDefHandler(member) {
    override def definesValue = flattensToEmpty(member.vparamss) // true if 0-arity
    override def resultExtractionCode(req: Request) =
      if (mods.isPublic) codegenln(name, ": ", req.typeOf(name)) else ""
  }

  abstract class MacroHandler(member: DefDef) extends MemberDefHandler(member) {
    override def referencedNames = super.referencedNames.flatMap(name => List(name.toTermName, name.toTypeName))
    override def definesValue = false
    override def definesTerm: Option[TermName] = Some(name.toTermName)
    override def definesType: Option[TypeName] = None
    override def resultExtractionCode(req: Request) = if (mods.isPublic) codegenln(notification(req)) else ""
    def notification(req: Request): String
  }

  class TermMacroHandler(member: DefDef) extends MacroHandler(member) {
    def notification(req: Request) = s"defined term macro $name: ${req.typeOf(name)}"
  }

  class AssignHandler(member: Assign) extends MemberHandler(member) {
    val Assign(lhs, rhs) = member
    override lazy val name = newTermName(freshInternalVarName())

    override def definesTerm = Some(name)
    override def definesValue = true
    override def extraCodeToEvaluate(req: Request) =
      """val %s = %s""".format(name, lhs)

    /** Print out lhs instead of the generated varName */
    override def resultExtractionCode(req: Request) = {
      val lhsType = string2code(req lookupTypeOf name)
      val res     = string2code(req fullPath name)
      """ + "%s: %s = " + %s + "\n" """.format(string2code(lhs.toString), lhsType, res) + "\n"
    }
  }

  class ModuleHandler(module: ModuleDef) extends MemberDefHandler(module) {
    override def definesTerm = Some(name.toTermName)
    override def definesValue = true

    override def resultExtractionCode(req: Request) = codegenln("defined object ", name)
  }

  class ClassHandler(member: ClassDef) extends MemberDefHandler(member) {
    override def definedSymbols = List(symbol, symbol.companionSymbol) filterNot (_ == NoSymbol)
    override def definesType = Some(name.toTypeName)
    override def definesTerm = Some(name.toTermName) filter (_ => mods.isCase)

    override def resultExtractionCode(req: Request) =
      codegenln("defined %s %s".format(keyword, name))
  }

  class TypeAliasHandler(member: TypeDef) extends MemberDefHandler(member) {
    private def isAlias = mods.isPublic && treeInfo.isAliasTypeDef(member)
    override def definesType = Some(name.toTypeName) filter (_ => isAlias)

    override def resultExtractionCode(req: Request) =
      codegenln("defined type alias ", name) + "\n"
  }

  class ImportHandler(imp: Import) extends MemberHandler(imp) {
    val Import(expr, selectors) = imp
    def targetType = intp.global.rootMirror.getModuleIfDefined("" + expr) match {
      case NoSymbol => intp.typeOfExpression("" + expr)
      case sym      => sym.thisType
    }
    private def importableTargetMembers = importableMembers(targetType).toList
    // wildcard imports, e.g. import foo._
    private def selectorWild    = selectors filter (_.name == nme.USCOREkw)
    // renamed imports, e.g. import foo.{ bar => baz }
    private def selectorRenames = selectors map (_.rename) filterNot (_ == null)

    /** Whether this import includes a wildcard import */
    val importsWildcard = selectorWild.nonEmpty

    def implicitSymbols = importedSymbols filter (_.isImplicit)
    def importedSymbols = individualSymbols ++ wildcardSymbols

    private val selectorNames = selectorRenames filterNot (_ == nme.USCOREkw) flatMap (_.bothNames) toSet
    lazy val individualSymbols: List[Symbol] = exitingTyper(importableTargetMembers filter (m => selectorNames(m.name)))
    lazy val wildcardSymbols: List[Symbol]   = exitingTyper(if (importsWildcard) importableTargetMembers else Nil)

    /** Complete list of names imported by a wildcard */
    lazy val wildcardNames: List[Name]   = wildcardSymbols map (_.name)
    lazy val individualNames: List[Name] = individualSymbols map (_.name)

    /** The names imported by this statement */
    override lazy val importedNames: List[Name] = wildcardNames ++ individualNames
    lazy val importsSymbolNamed: Set[String] = importedNames map (_.toString) toSet

    def importString = imp.toString
    override def resultExtractionCode(req: Request) = codegenln(importString) + "\n"
  }
}