Multiple packages definition

Question

While browsing the source code of the Scala API, I met this package definition in scala/tags/R_2_8_0_final/src/library/scala/util/parsing/combinator/syntactical/StdTokenParsers.scala:

package scala.util.parsing
package combinator
package syntactical

What does that mean? That the class will be available in more than one package?

Answer 1

The Scala reference mentions (chapter 9, section 9.1):

A compilation unit consists of a sequence of packagings, import clauses, and class and object definitions, which may be preceded by a package clause.

A compilation unit

package p1;
...
package pn;
stats

starting with one or more package clauses is equivalent to a compilation unit consisting of the packaging

package p1 { ...
  package pn {
   stats
  } ...
}

See also Organizing Code in Files and Namespaces on nested packages.
(From Programming Scala: Scalability = Functional Programming + Objects By Dean Wampler, Alex Payne, page 44, Chapter 2)

Answer 2

This is basically the same as

package scala.util.parsing.combinator.syntactical

import scala.util.parsing._
import scala.util.parsing.combinator._

...

So by "stacking" the packages the way you wrote you can get super-packages in scope. See also these answers.

[Update] Here is a new article written by Martin Odersky about this topic: http://www.artima.com/scalazine/articles/chained_package_clauses_in_scala.html