Is there any way to extend an object?

In scala, we cannot extend object:

object X 
object Y extends X

gives an error error: not found: type X

In my case someone has defined some functionality in an object and I need to extend it (basically add another method). What would be the easiest way to extend this object?

Solution 1:

As so often the correct answer depends on the actual business requirement. Extending from an object would in some sense defy the purpose of that object since it wouldn't be a singleton any longer.

What might be a solution is to extract the behavior into an abstract trait. And create objects extending that trait like so:

trait T{
    // some behavior goes here
}

object X extends T

object Y extends T {
    // additional stuff here
}

Solution 2:

If you want use methods and values from another object you can use import.

object X{
  def x = 5
}

object Y{
  import X._
  val y = x
}

Solution 3:

You can't actually extend an object, because that would create two of it, and an object by definition exists only once (edit: well, that's not quite true, because the object definition can be in a class or method).

For your purposes, try this:

object X {
}

object Y {
    def a = 5
}

implicit def xToY(x: X.type) = Y

println(X.a)

It doesn't actually extend, but it does allow you to call new methods on it than were originally defined.