Generics, WTF?

Generics are complicated, and that ties into some esoteric-looking Kotlin syntax that we will explore much later in the book:

• When you see the out keyword, such as in class Something<out T>, that is Kotlin’s approach for declaring “covariance”, stipulating that an instance of Something is allowed to produce T objects (e.g., return them from functions) but not consume them (e.g., accept them as parameters)
• When you see the in keyword, such as in class Something<in T>, that is Kotlin’s approach for declaring “contravariance”, stipulating that an instance of Something is allowed to consume T objects but not produce them
• When you see <reified T>… well, that is difficult to explain