The weirdest thing with the new breed of strongly typed language, in my opinion, is that they naturally accept sum types, which are completely alien from an OOP

The weirdest thing with the new breed of strongly typed language, in my opinion, is that they naturally accept sum types, which are completely alien from an OOP point of view. I mean, the magnificiently useful case switch feature you have in most of those new languages translates very awkwardly in, say, Java by using a isinstanceof then some kind of cast, which I gather is Considered Harmful because it breaks encapsulation and type safety, yet case switches are a natural consequence of sum types, and are completely safe, in the context of a type system that have sum types. Switching on "type" also happens to be a thing I see a lot in what one would traditionally consider bad code, for example, treating a scalar and an array differently in PHP, or having functions that can deal with many different shapes and kinds of JSON blobs in JavaScript. There also have been a lot of hype around the idea of eliminating null references by using Maybe types, which in the end are just a degenerate case of a sum type. My pet theory is that the ability to keep doing this in a safe and formalized manner is what makes the new breed of statically typed PLs so cool.