factory_init.swift

protocol Factory {
    init(factory: () -> Self)
}
extension Factory {
    init(factory: () -> Self) {
        self = factory()
    }
}
class Animal {
    var emoji: Character { return "❓" }
}

class Cat : Animal {
    override var emoji: Character { return "🐱" }
}

class Dog : Animal {
    override var emoji: Character { return "🐶" }
}

extension Animal : Factory {
    convenience init(type: String) {
        self.init(factory: {
            switch type {
            case "dog": return Dog()
            case "cat": return Cat()
            default: return Animal()
            }
        })
    }
}