I agree, ownership is an important idea on its own. So I wish more mainstream gc languages would expose some kind of optional ownership idea. Such as ability to "give" a collection to another collection contructor, which then would not have to do a boilerplatey/inefficient "safe-copy" in the contructor. Maybe that opens a can of worms and can't be easily retrofitted into existing languages, I don't know, but I'd like to see it tried.