おもしろい
class AnimalError: Error {} class CatError: AnimalError {} do { let never: () -> Void = {} let cat: () throws(CatError) -> Void = never let animal: () throws(AnimalError) -> Void = cat let creature: () throws -> Void = animal } do { let creature: (() throws -> Void) -> Void = { _ in } let animal: (() throws(AnimalError) -> Void) -> Void = creature let cat: (() throws(CatError) -> Void) -> Void = animal let never: (() -> Void) -> Void = cat }