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You can do this in Java using derive4j: https://github.com/derive4j/derive4j https://github.com/derive4j/derive4j. It generates code for algebraic data types w

• Latty 9y ago
  In the same way you could "do" lambdas with single method interfaces in Java pre-8. It was possible, but it was still a pain to do.
  • jbgi 9y ago
    It depends. Bare minimum, in scala you have to do: sealed trait Either[A, B] final case class Left[A, B](a: A) extends Either[A, B] final case class Right[A, B](b: B) extends Either[A, B] and it is still not a real sum type due to exposing subtyping (cf. https://github.com/quasar-analytics/quasar/wiki/Faking-Sum-Types https://github.com/quasar-analytics/quasar/wiki/Faking-Sum-T...) with derive4j: @Data interface Either<A, B> { <X> X match(Function<A, X> left, Function<B, X> right); } or, at your preference: @Data interface Either<A, B> { interface Cases<X> { X left(A leftValue); X right(B rightValue); } <X> X match(Cases<X> cases); } So it is actually not much boilerplate. The real drawback of (any) java implementation is lack of TCO.