Hands-On Design Patterns with Swift

Closure-based type erasure

The final step in our closure-based type erasure is to implement the initializer that will be used to wrap Cows and Goats:

final class AnyAnimal<T>: Animal where T: Food {    typealias FoodType = T    private let eatBlock: (T) -> Void        init<A: Animal>(animal: A) where A.FoodType == T {        eatBlock = animal.eat    }    func eat(food: T) {        eatBlock(food)    }}

Let's sum up the changes:

• We marked the class final to avoid any wrong usage.
• We added an eatBlock: (T) -> Void property to capture the eat method from the animal.
• We added an implementation to func eat(food: T) to forward the calls to the original method.
• We added the generic initializer that also binds the T type to FoodType of the provided Animal type, A.FoodType.

Let's ...