Scala example source code file (Util.scala)

This example Scala source code file (Util.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, context, list, literal, parallel, select, stringcontext, termname, util

The Util.scala Scala example source code

package scala.tools.partest

import scala.language.experimental.macros

object Util {
  /**
   * `trace("".isEmpty)` will return `true` and as a side effect print the following to standard out.
   * {{{
   *   trace> "".isEmpty
   *   res: Boolean = true
   *
   * }}}
   *
   * An alternative to [[scala.tools.partest.ReplTest]] that avoids the inconvenience of embedding
   * test code in a string.
   */
  def trace[A](a: A) = macro traceImpl[A]

  import scala.reflect.macros.blackbox.Context
  def traceImpl[A: c.WeakTypeTag](c: Context)(a: c.Expr[A]): c.Expr[A] = {
    import c.universe._
    import definitions._

    // xeno.by: reify shouldn't be used explicitly before the final release of 2.10.0,
    // because this impairs reflection refactorings
    //
    // val exprCode = c.literal(show(a.tree))
    // val exprType = c.literal(show(a.actualType))
    // reify {
    //   println(s"trace> ${exprCode.splice}\nres: ${exprType.splice} = ${a.splice}\n")
    //   a.splice
    // }

    c.Expr(Block(
      List(Apply(
        Select(Ident(PredefModule), TermName("println")),
        List(Apply(
          Select(Apply(
            Select(Ident(ScalaPackage), TermName("StringContext")),
            List(
              Literal(Constant("trace> ")),
              Literal(Constant("\\nres: ")),
              Literal(Constant(" = ")),
              Literal(Constant("\\n")))),
          TermName("s")),
          List(
            Literal(Constant(show(a.tree))),
            Literal(Constant(show(a.actualType))),
            a.tree))))),
      a.tree))
  }
}