Thanks for your comment! Yes and no. CassandraSerializable is a type class for types that can be serialized with Cassandra. In the end i used Any because i leave it to clients to either use List[T:CassandraSerializable] or a single T:CassandraSerializable (i know the syntax is incorrect here, but this is to demonstrate what i wanted to have). I will check that the scala union type simulation described in http://www.chuusai.com/2011/06/09/scala-union-types-curry-howard/ can be used in conjunction with type classes. If yes, i will use a union type here.