Hands-On Design Patterns with Swift

The private box

The private box will be a type that implements the abstract base class. The goal of the private box is to provide a wrapper around the concrete object implementing the PAT and forward all of the calls to the boxed object.

Following the conventions also suggests that you should use _Any#MY_PROTOCOL#Box as a class name for this component:

private final class _AnyAnimalBox<A: Animal>: _AnyAnimalBase<A.FoodType> {    // The target object, that is an Animal    var target: A    init(_ target: A) {        self.target = target    }        // Overrides of the abstract classes's implementation    // Forward all invocations to the concrete target    override var name: String {        return target.name    }    override var preferredFood: A.FoodType? {        get { return target.preferredFood ...