It's funny to see that singleton types are within the highest level: 'expert'. While in Typescript they're, together with union types, the most intuïtive thing ever. I guess that's because to express them in a language that doesn't have native support requires advanced deftness in typelevel programming. Like f.i. implementing them yourself in Scala 2.x. So I expect the coolness factor of singleton types and union types to fall precipitously as soon as Scala 3.x/Dotty becomes prevalent. They'll be 'just' a powerful feature that everybody understands and uses all the time.