Preferred way of grouping utility functions in Scala?

Question

What's the best way of grouping utility functions that don't belong in a class? In Ruby, I would have grouped them in a module. Should I use traits in Scala for the same effect, or objects?

Answer 1

Usually, I put utility functions that are semantically different into different traits and create an object for each trait, e.g.

trait Foo {
  def bar = 1
}
object Foo extends Foo

That way I'm most flexible. I can import the utility functions via an import statement or via with in the class declaration. Moreover I can easily group different utility traits together into a new object to simplify the import statements for the most commonly used utility functions, e.g.

object AllMyUtilites extends Foo with Foo2

Answer 2

Package objects or just plain objects.

See, for instance, Scala.Predef and scala.math.

Answer 3

Traits if you want them to be mixed in with the classes that are going to use it. Objects if you want to only have to import them.