I'd say "yes" only because this concept will exist whether or not you have a name for it. And it's a concept you will bump into in any language with any sort of

I'd say "yes" only because this concept will exist whether or not you have a name for it. And it's a concept you will bump into in any language with any sort of generics (even Go [1]) I wrote Scala for the last 2 years and was the resident type system "expert", so I had to explain variance to people pretty often. Luckily, it's a pretty quick, mathy definition: Some notation first: A <: B means "A is a subtype of B" A >: B means "A is a supertype of B" F[_] refers to a unary type constructor. Now for the definitions: If F[_] is "covariant", it means that if A <: B, then F[A] <: F[B] If F[_] is "contravariant", it means that if A >: B, then F[B] <: F[A] Examples of covariant type constructors are List and Functions in their output. An example of a contravariant type constructor is Functions in their input type. ^ This is all that needs to be said! I can write it on a whiteboard in ~5 minutes. I'd say that's a reasonable thing to be expected to learn. [1] https://www.reddit.com/r/golang/comments/3gtg3i/passing_slice_of_values_as_slice_of_interfaces/ https://www.reddit.com/r/golang/comments/3gtg3i/passing_slic...