工厂模式（Swift 实现）

Factory Method 工厂模式

Provide the method for creating an instance in the superclass, and allow the subclass to choose the type of the instance.

在父类中提供创建对象的方法，允许子类决定实例化对象的类型。

具备的部分：生产者协议、产品协议，往后就可以根据需要来扩展每一种产品。

具体的生产者比如 MongoCakeCreator 的存在是为了实现与产品相关的核心业务逻辑，而不仅仅是创建 MongoCake 实例。工厂方法将核心业务逻辑从具体产品类中分离出来。

// Creator
protocol CakeCreator {
    
    func createCake() -> Cake
    func doSomethingForCake(cake: Cake) -> Cake
}

// Product
protocol Cake {
    
    func doWork()
}

// ConcreteCreator
class MongoCakeCreator: CakeCreator {
    
    var cake: MongoCake?
    func createCake() -> Cake {
    
        var cake = MongoCake()
        doSomethingForCake(cake: cake)
        return cake
    }
    func doSomethingForCake(cake: Cake) -> Cake{
    
        cake.doWork()
        cake.doWork()
        return cake
    }
    
}

// ConcreteCreator
class ChocolateCakeCreator: CakeCreator {
    
    func createCake() -> Cake {
    
        var cake = ChocolateCake()
        doSomethingForCake(cake: cake)
        return cake
    }
    
    func doSomethingForCake(cake: Cake) -> Cake{
    
        cake.doWork()
        return cake
    }
}

class MongoCake: Cake {
    
    func doWork() {
    
        print("Add some mongo")
    }
}

class ChocolateCake: Cake {
    
    func doWork() {
    
        print("Add some chocolate")
    }
}

// If we want to add a type of cake call "PinapleCake", just need to 
// make it conform to Cake and add a creator that conform to the CakeCreator for the "PinapleCake"

let cakeOne = MongoCakeCreator().createCake()