sampletransform.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 49 行

/* NSC -- new Scala compiler
 * Copyright 2005-2006 LAMP/EPFL
 * @author Martin Odersky
 */
// $Id: SampleTransform.scala 8406 2006-08-17 14:11:13Z michelou $

package scala.tools.nsc.transform

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

  import global._                  // the global environment
  import definitions._             // standard classes and methods
  import typer.{typed, atOwner}    // methods to type trees
  import posAssigner.atPos         // for filling in tree positions 

  /** 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}
          copy.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'
                    tree1.pos,
                    newTermName("sample"))))))  // The standard term name creator
        case _ =>
          tree1
      }
    }
  }
}