Scala: Importing packages into package objects

Question

I'm having trouble importing packages into package objects. It didn't seem to work in Eclipse and so I switched to intellij. At one point the feature seemed to be working and so I created package objects for most packages. Now it doesn't seem to be working at all. Here's a package object in file package.scala, the package file itself compiles fine:

package rStrat.rSwing
package testSw //Edited for clarity

object testSw
{
  import rStrat._
  import rSwing.topUI._
}

and here's a class file from the same module and package.

package rStrat.rSwing.testSw

object MainTest {
  def main(args: Array[String])
  {
    val testApp = new AppWindow //Appwindow is a member of topUI
    testApp.open
  }
}

It works fine if I import the topUI package straight into the MainTest file. it makes no difference whether I try and import the whole package or a particular class. is this legal scala? Is the problem with the IDEs?

I'm using Scala 2.92 Final, Intellij 11.1.1, JDK 1.6.0_31, Eclipse 3.7.2

No you had my hopes up there for a moment. It doesn't seem to make any difference. — Rich Oliver, May 09 '12 at 18:40
Place `package object testSw` in a file with declaration `rStrat.rSwing`. — ziggystar, May 09 '12 at 18:44
@ziggystar What do you mean by declaration? I can't import rStrat.rSwing._ because I get an ambiguous reference error. I can split up the package line at the top of the file but it makes no difference. — Rich Oliver, May 09 '12 at 19:00
Remove the second line. See here: http://www.scala-lang.org/docu/files/packageobjects/packageobjects.html — ziggystar, May 09 '12 at 19:48
@ziggystar No I'd already tried that. I tried it again in more than one place but still no joy. — Rich Oliver, May 09 '12 at 20:11

score 4 · Accepted Answer · answered May 09 '12 at 20:28

4

Scala does not have first class imports. Where a package can only contain declarations of classes and traits, a package object can contain any other valid Scala declaration like var, val, def, type (type alias), implicit stuff. And although as in any object you can import things, they don't transitively propagate to the rest of the package and are thus not visible to the rest of the world.

answered May 09 '12 at 20:28

agilesteel

16,775
6
44
55

Ah that's a damn shame particularly as we lost automatic inclusion of outer packages in 2.8. One thing I always wanted in C# was an include statement to get a kind of multiple namespace inheritance. – Rich Oliver May 09 '12 at 20:58
1

Check out [this link](http://www.artima.com/scalazine/articles/selfless_trait_pattern.html). To be honest it's not what you want, but maybe it will point you to some alternative ideas... – agilesteel May 09 '12 at 21:06

score 3 · Answer 2 · answered May 09 '12 at 23:19

This creates the object rStrat.rSwing.testSw.testSw:

package rStrat.rSwing
package testSw //Edited for clarity

object testSw

This creates the package object rStrat.rSwing.testSw.testSw:

package rStrat.rSwing
package testSw //Edited for clarity

package object testSw

This creates the package object rStrat.rSwing.testSw:

package rStrat.rSwing

package object testSw

It's the last one you want.

Scala: Importing packages into package objects

2 Answers2

Linked