For "Box[+T]", can I say "The type Box is covariant", is it correct?

Question

Say I defined a type constructor Box:

trait Box[+T]

What is correct?

1. type Box is covariant
2. type constructor Box is covariant
3. type parameter T is covariant
4. type parameter T in type constructor Box is covariant
5. If all of them are incorrect, what's the correct expression?

Answer 1

About variance from the book Functional Programming in Scala:

In the declaration trait List[+A], the + in front of the type parameter A is a variance annotation which signals that A is a covariant or “positive” parameter of List. This means that, for instance, List[Dog] is considered a subtype of List[Animal] , assuming Dog is a subtype of Animal.