Singleton Object vs Companion Object in Class

Question

I have written the following code:

class a {

  object c {
    var a = "STATIC"

    def m() = print("STATIC METHOD")

    var f = () => print("STATIC FUNCTION")
  }

}

object m {
  def main(args: Array[String]) = {
    var o = new a()
    o.c.m()
  }
}

1. Can I say that the variables, functions and methods that are declared in object c can be static?
2. If I change name of object c with a then will the object becomes a companion object?

Answer 1

Scala has no true meaning of 'static' that Java does.

The fact that objects have a backing on the JVM that uses static methods / fields is a leaking implementation detail that you only need to deal with if using Java/JVM interop.

Unless you explicitly need that interop, you need to stop thinking of declared objects as 'static' and instead think of them as singletons within their given scope.

An inner object nested under a class, means that there is only ever going to be 1 instance of that object, for each class instance, unlike inner classes which could have multiple instances.

This applies at the top level as well, except that Scala can do additional compatibility with other JVM languages, and mark some of the methods/members as static.