Scala example source code file (PostErasure.scala)

This example Scala source code file (PostErasure.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

b, compilationunit, compiler, global, infotransform, nsc, old, posterasure, posterasuretransformer, string, symbol, tree

The PostErasure.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author Martin odersky
 */
package scala.tools.nsc
package transform

/** This phase maps ErasedValueTypes to the underlying unboxed representation and
 *  performs peephole optimizations.
 */
trait PostErasure extends InfoTransform with TypingTransformers with scala.reflect.internal.transform.PostErasure {
  val global: Global

  import global._
  import treeInfo._

  val phaseName: String = "posterasure"

  def newTransformer(unit: CompilationUnit): Transformer = new PostErasureTransformer(unit)
  override def changesBaseClasses = false

  class PostErasureTransformer(unit: CompilationUnit) extends TypingTransformer(unit) {
    override def transform(tree: Tree) = {
      def finish(res: Tree) = logResult(s"Posterasure reduction\n  Old: $tree\n  New")(res)

      /* We use the name of the operation being performed and not the symbol
       * itself because the symbol hails from the boxed class, and this transformation
       * exists to operate directly on the values. So we are for instance looking
       * up == on an lhs of type Int, whereas the symbol which has been passed in
       * is from java.lang.Integer.
       */
      def binop(lhs: Tree, op: Symbol, rhs: Tree) =
        finish(localTyper typed (Apply(Select(lhs, op.name) setPos tree.pos, rhs :: Nil) setPos tree.pos))

      super.transform(tree) setType elimErasedValueType(tree.tpe) match {
        case AsInstanceOf(v, tpe) if v.tpe <:< tpe => finish(v)          // x.asInstanceOf[X]       ==> x
        case ValueClass.BoxAndUnbox(v)             => finish(v)          // (new B(v)).unbox        ==> v
        case ValueClass.BoxAndCompare(v1, op, v2)  => binop(v1, op, v2)  // new B(v1) == new B(v2)  ==> v1 == v2
        case tree                                  => tree
      }
    }
  }
}