Dual package statements in Scala

Question

I have seen in a few libraries, Spray for example, dual package specifications like this:

package cc.spray
package http

// code

Is this just eye candy for package cc.spray.http, or is there a functional benefit to breaking the two apart like this?

score 8 · Accepted Answer · answered Jun 15 '12 at 21:47

8

That is equivalent to this:

package cc.spray.http
import cc.spray._
// implicitly, import cc.spray.http._

That is, every member of package cc.spray and of package cc.spray.http are visible. On the other hand, members of the package cc are not visible.

This way one can safely use names such as java in their package hierarchy without causing trouble, and, at the same time, easily make visible the package scopes one wants to be visible.

answered Jun 15 '12 at 21:47

Daniel C. Sobral

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Just when you think you start to know a language, something know and cool shows up... – Dave Griffith Jun 16 '12 at 00:00

score 3 · Answer 2 · answered Jun 15 '12 at 21:24

3

The separate package statements puts both cc.spray and cc.spray.http in scope.

answered Jun 15 '12 at 21:24

leedm777

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virtualeyes · Answer 3 · 2012-06-17T08:26:32.633

1

let's not forget one nice win gained from this approach

// Foo.scala
package cc.spray
package http

class Foo {
  ...
}

// Bar.Scala
package cc.spray
package bar

import http._ // concise imports relative to cc.spray

class Bar {
  ...
}

edited Jun 17 '12 at 08:26

answered Jun 17 '12 at 08:20

virtualeyes

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score 0 · Answer 4 · answered Jun 16 '12 at 13:24

Like a lot of other things, this was introduced with Scala 2.8: the other answers give you the "what" (exposing multiple package scopes to the current context) and the official Scala doc has a lot more detail, along with a detailed rationale for the feature.

Dual package statements in Scala

4 Answers4