What I really wish is that we had a popular language with support for existential types. They provide a very nice way of unifying OOP-style encapsulation with

What I really wish is that we had a popular language with support for existential types. They provide a very nice way of unifying OOP-style encapsulation with FP-style parametric polymorphism and generic programming. For more info, see the docs for the Haskell extension: https://wiki.haskell.org/Existential_type https://wiki.haskell.org/Existential_type