Companion

Creates a contravariant projection of a given type, denoted by the in modifier applied to a type. For example, in the type MutableList<in Number>, in Number is a contravariant projection of the type of class Number.

Creates a covariant projection of a given type, denoted by the out modifier applied to a type. For example, in the type Array<out Number>, out Number is a covariant projection of the type of class Number.

Creates an invariant projection of a given type. Invariant projection is just the type itself, without any use-site variance modifiers applied to it. For example, in the type Set<String>, String is an invariant projection of the type represented by the class String.