Why do people define object extends its companion class?

Question

I find this kind of code is very common in Lift framework, written like this:
object BindHelpers extends BindHelpers {} What does this mean?

Answer 1

In this case, BindHelpers is a trait and not a class. Let foo() to be a method defined in BindHelpers, to access it you can either.

1. Use it through the companion object: BindHelpers.foo()

2. Mix the trait BindHelpers in a class and thus be able to access the methods inside of it.

For instance:

class MyClass extends MyParentClass with BindHelpers {
  val a = foo()
}

The same techniques is used in Scalatest for ShouldMatchers for instance.

Answer 2

You can find David Pollak's answer to the same question in the liftweb group.