The problem with this is that any time you add a subclass to Animal, you need to manually update AnyAnimal to handle it. It’s possible to do this more generica

The problem with this is that any time you add a subclass to Animal, you need to manually update AnyAnimal to handle it. It’s possible to do this more generically, because you know the animal’s type in the AnyAnimal constructor and that’s sufficient to declare its subsequent behavior: struct AnyAnimal: Animal { let name: String private let walker: () -> Void private let eater: (Any) -> Void init<T: Animal>(_ animal: T) { name = animal.name walker = { animal.walk() } eater = { food in guard let f = food as? T.FoodType else { return } animal.eat(food: f) } } func walk(){ walker() } func eat(food: Any){ eater(food) } }