The mutable collection's factory method 'empty[T]' should have parenthesis

[kmizu]

For example, an instance of scala.collection.mutable.Buffer can be created via:

val buffer = scala.collection.mutable.Buffer.empty[Int]

Since this method returns a different buffer for each call, it has side effect. Then, this method should be called as the followings:

val buffer = scala.collection.mutable.Buffer.empty[Int]()

However, since empty[T] method is declared as 'no parentheses' method, it cannot be done. I think it should be fixed. How do you think about it?

[lrytz]

We discussed this at scala/collection-strawman#520. Please re-open if you think that it needs further discussion.