DogHandler.swift

class DogHandler: Handler {
    func handle(request: Animal) {
        if request > .dog {
            next?.handle(request: request)
        } else {
            print ("Handled by the dog handler")
        }

    }
    var next: Handler?
}

class WolfHandler: Handler {
    func handle(request: Animal){
        if request > .wolf {
            next?.handle(request: request)
        } else {
            print ("Handled by the wolf handler")
        }
    }
    var next: Handler?
}

class ElephantHandler: Handler {
    func handle(request: Animal){
        if request > .elephant {
            next?.handle(request: request)
        } else {
            print ("Handled by the elephant handler")
        }
    }
    var next: Handler?
}