Scala example source code file (SampleTransform.scala)

This example Scala source code file (SampleTransform.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

a, block, compilationunit, compiler, nsc, sampletransformer, select, super, the, transformer, tree, trees

The SampleTransform.scala Scala example source code

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

package scala.tools.nsc
package transform

/** A sample transform.
 */
abstract class SampleTransform extends Transform {
  // inherits abstract value `global` and class `Phase` from Transform

  import global._       // the global environment
  import typer.typed    // method to type trees

  /** the following two members override abstract members in Transform */
  val phaseName: String = "sample-phase"

  protected def newTransformer(unit: CompilationUnit): Transformer =
    new SampleTransformer(unit)

  class SampleTransformer(unit: CompilationUnit) extends Transformer {

    override def transform(tree: Tree): Tree = {
      val tree1 = super.transform(tree);      // transformers always maintain `currentOwner`.
      tree1 match {
        case Block(List(), expr) =>           // a simple optimization
          expr
        case Block(defs, sup @ Super(qual, mix)) => // A hypthothetic transformation, which replaces
                                                    // {super} by {super.sample}
          treeCopy.Block(                           // `copy` is the usual lazy tree copier
            tree1, defs,
            typed(                              // `typed` assigns types to its tree argument
              atPos(tree1.pos)(                 // `atPos` fills in position of its tree argument
                Select(                         // The `Select` factory method is defined in class `Trees`
                  sup,
                  currentOwner.newValue(        // creates a new term symbol owned by `currentowner`
                    newTermName("sample"),      // The standard term name creator
                    tree1.pos)))))
        case _ =>
          tree1
      }
    }
  }
}