Scala example source code file (FastTrack.scala)

This example Scala source code file (FastTrack.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

applied, compiler, emptytree, fasttrackentry, macroargs, macrocontext, nil, nsc, partialfunction, quasiquoteimpls, reflection, reify, symbol, tree

The FastTrack.scala Scala example source code

package scala.tools
package reflect

import scala.reflect.reify.Taggers
import scala.tools.nsc.typechecker.{ Analyzer, Macros }
import scala.reflect.runtime.Macros.currentMirror
import scala.reflect.api.Universe
import scala.tools.reflect.quasiquotes.{ Quasiquotes => QuasiquoteImpls }

/** Optimizes system macro expansions by hardwiring them directly to their implementations
 *  bypassing standard reflective load and invoke to avoid the overhead of Java/Scala reflection.
 */
class FastTrack[MacrosAndAnalyzer <: Macros with Analyzer](val macros: MacrosAndAnalyzer) {

  import macros._
  import global._
  import definitions._
  import scala.language.implicitConversions
  import treeInfo.Applied

  def contains(symbol: Symbol): Boolean = fastTrackCache().contains(symbol)
  def apply(symbol: Symbol): FastTrackEntry = fastTrackCache().apply(symbol)
  def get(symbol: Symbol): Option[FastTrackEntry] = fastTrackCache().get(symbol)

  private implicit def context2taggers(c0: MacroContext): Taggers { val c: c0.type } =
    new { val c: c0.type = c0 } with Taggers
  private implicit def context2macroimplementations(c0: MacroContext): FormatInterpolator { val c: c0.type } =
    new { val c: c0.type = c0 } with FormatInterpolator
  private implicit def context2quasiquote(c0: MacroContext): QuasiquoteImpls { val c: c0.type } =
    new { val c: c0.type = c0 } with QuasiquoteImpls
  private def makeBlackbox(sym: Symbol)(pf: PartialFunction[Applied, MacroContext => Tree]) =
    sym -> new FastTrackEntry(pf, isBlackbox = true)
  private def makeWhitebox(sym: Symbol)(pf: PartialFunction[Applied, MacroContext => Tree]) =
    sym -> new FastTrackEntry(pf, isBlackbox = false)

  final class FastTrackEntry(pf: PartialFunction[Applied, MacroContext => Tree], val isBlackbox: Boolean) extends (MacroArgs => Any) {
    def validate(tree: Tree) = pf isDefinedAt Applied(tree)
    def apply(margs: MacroArgs): margs.c.Expr[Nothing] = {
      val MacroArgs(c, _) = margs
      // Macros validated that the pf is defined here - and there's not much we could do if it weren't.
      c.Expr[Nothing](pf(Applied(c.expandee))(c))(c.WeakTypeTag.Nothing)
    }
  }

  /** A map from a set of pre-established macro symbols to their implementations. */
  private val fastTrackCache = perRunCaches.newGeneric[Map[Symbol, FastTrackEntry]] {
    val runDefinitions = currentRun.runDefinitions
    import runDefinitions._
    Map[Symbol, FastTrackEntry](
      makeBlackbox(        materializeClassTag) { case Applied(_, ttag :: Nil, _)                 => _.materializeClassTag(ttag.tpe) },
      makeBlackbox(     materializeWeakTypeTag) { case Applied(_, ttag :: Nil, (u :: _) :: _)     => _.materializeTypeTag(u, EmptyTree, ttag.tpe, concrete = false) },
      makeBlackbox(         materializeTypeTag) { case Applied(_, ttag :: Nil, (u :: _) :: _)     => _.materializeTypeTag(u, EmptyTree, ttag.tpe, concrete = true) },
      makeBlackbox(           ApiUniverseReify) { case Applied(_, ttag :: Nil, (expr :: _) :: _)  => c => c.materializeExpr(c.prefix.tree, EmptyTree, expr) },
      makeBlackbox(            StringContext_f) { case _                                          => _.interpolate },
      makeBlackbox(ReflectRuntimeCurrentMirror) { case _                                          => c => currentMirror(c).tree },
      makeWhitebox(  QuasiquoteClass_api_apply) { case _                                          => _.expandQuasiquote },
      makeWhitebox(QuasiquoteClass_api_unapply) { case _                                          => _.expandQuasiquote }
    )
  }
}