Hands-On Design Patterns with Swift

Boxing-based type erasure

The boxing-based type erasure pattern requires three distinct objects: 

• An abstract base class
• A private box, which will inherit the abstract base class
• A public wrapper

As for the public wrapper, we can reuse the one that we wrote above AnyAnimal<T>.

In order to make the exercise a bit more interesting, let's change the Animal protocol to introduce some complexities such as the animal's preferred food and name:

protocol Animal {    associatedtype FoodType: Food    var preferredFood: FoodType? { get set }    var name: String { get }    func eat(food: FoodType)}

Reflecting the changes in the Animal protocol, we need to update AnyAnimal. Let's not bother too much with the initializers now, as we'll implement them as we go: