Scala composing package objects

Question

I'm working on some tooling that'll be loaded in the standard repl, or ammonite. Is there any way to compose package objects / imports so that I don't have to import the scala.concurent.duration package in my clients ? Is this the only way for me to reuse the implicit duration conversion ?

(yes I know an ammonite script wrapping my tooling can load everything for the REPL but ammonite might not be the only way I use the packages)

This wouldn't be a scaleable approach :(

package object tool package {
  // redeclaring the implicit value class conversions found in package object scala.concurrent.duration
  implicit final class DurationInt(private val n: Int) extends AnyVal with DurationConversions {
    override protected def durationIn(unit: TimeUnit): FiniteDuration = Duration(n.toLong, unit)
  }

  implicit final class DurationLong(private val n: Long) extends AnyVal with DurationConversions {
    override protected def durationIn(unit: TimeUnit): FiniteDuration = Duration(n, unit)
  }
}

som-snytt · Accepted Answer · 2016-09-09 17:56:20Z

Yes. Folks ask to "package imports" in this way, but it doesn't work that way.

Another common use case is importing the language implicits: you must redefine the values in your package.

The following doesn't work in REPL, but putting it here as a reminder for future:

scala> :pa -raw
// Entering paste mode (ctrl-D to finish)

// attempt to add an import into the block
package object w {
  def wrap[A](a: A): A = macro www[A]
  import reflect.macros.blackbox.Context
  def www[A: c.WeakTypeTag](c: Context)(a: c.Expr[A]) = {
    import c.universe._
    val Block(ss, res) = a.tree
    Block(q"import scala.concurrent.duration._" +: ss, res)
  }
}

// Exiting paste mode, now interpreting.


scala> $intp.setExecutionWrapper("w.wrap")

It doesn't work because the wrapper wraps the wrong bit of code...

scala> 5.seconds
<console>:12: error: value seconds is not a member of Int
       5.seconds
         ^

scala> :se -Xprint:typer

scala> 42
[[syntax trees at end of                     typer]] // <console>
package $line7 {
  object $read extends scala.AnyRef {
    def <init>(): $line7.$read.type = {
      $read.super.<init>();
      ()
    };
    object $iw extends scala.AnyRef {
      def <init>(): type = {
        $iw.super.<init>();
        ()
      };
      object $iw extends scala.AnyRef {
        def <init>(): type = {
          $iw.super.<init>();
          ()
        };
        private[this] val res4: Int = 42;
        <stable> <accessor> def res4: Int = $iw.this.res4
      }
    }
  }
}

[[syntax trees at end of                     typer]] // <console>
package $line7 {
  object $eval extends scala.AnyRef {
    def <init>(): $line7.$eval.type = {
      $eval.super.<init>();
      ()
    };
    lazy private[this] var $result: Int = _;
    <stable> <accessor> lazy def $result: Int = {
      $eval.this.$result = $line7.$read.$iw.$iw.res4;
      $eval.this.$result
    };
    lazy private[this] var $print: String = _;
    <stable> <accessor> lazy def $print: String = {
      $eval.this.$print = ({
        import scala.concurrent.duration._;
        $line7.$read.$iw.$iw;
        "res4: Int = ".+(scala.runtime.ScalaRunTime.replStringOf($line7.$read.$iw.$iw.res4, 1000))
      }: String);
      $eval.this.$print
    }
  }
}

res4: Int = 42

...and anyway the code must compile before and after expansion.

The templating doesn't allow adding the trailing brace:

scala> $intp.setExecutionWrapper("{ import scala.concurrent.duration._ ")

It would have to look something like

scala> $intp.setExecutionWrapper("{ import scala.concurrent.duration._ %s }")

As you point out, scala -i my-imports.sc is for the general init, but something with fewer seams would be neat.

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