This is the sixth of a series of articles on “Type Parameters and Type Members”. If you haven’t yet, you should start at the beginning, which introduces code we refer to throughout this article without further ado. In a subtyping language such as Java or Scala, first-class existentials are a helpful ally for modeling values and methods that abstract over subtypes in different ways. In a language with mutation, such as Java or Scala, existentials help deal with certain kinds of state cha...
