Is there any way to extend an object?

Question

In scala, we cannot extend object:

object X 
object Y extends X

gives an error error: not found: type X

I

Answer 1

Note that with Dotty (foundation of Scala 3), you can alternatively use composition (instead of inheritance) via export clauses which allow defining aliases for selected members of an object:

object X { def f = 5 }

object Y {
  export X._
  def g = 42
  def h = f * g
}

Y.f // 5
Y.g // 42
Y.h // 210

Note that you can also restrict which members you want to export:

object X { def f = 5; def g = 6 }
object Y { export X.f }
Y.f // 5
Y.g
^^^
value g is not a member of Y