工厂方法

🏭 Factory Method

The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time.(使用工厂模式取代类构造函数,抽象对象生成过程,对象实例化的类型可以在运行时决定。)

/*:
### Example
*/
protocol Currency {
    func symbol() -> String
    func code() -> String
}

class Euro : Currency {
    func symbol() -> String {
        return "€"
    }
    
    func code() -> String {
        return "EUR"
    }
}

class UnitedStatesDolar : Currency {
    func symbol() -> String {
        return "$"
    }
    
    func code() -> String {
        return "USD"
    }
}

enum Country {
    case unitedStates, spain, uk, greece
}

enum CurrencyFactory {
    static func currency(for country:Country) -> Currency? {

        switch country {
            case .spain, .greece :
                return Euro()
            case .unitedStates :
                return UnitedStatesDolar()
            default:
                return nil
        }
        
    }
}
/*:
### Usage
*/
let noCurrencyCode = "No Currency Code Available"

CurrencyFactory.currency(for: .greece)?.code() ?? noCurrencyCode
CurrencyFactory.currency(for: .spain)?.code() ?? noCurrencyCode
CurrencyFactory.currency(for: .unitedStates)?.code() ?? noCurrencyCode
CurrencyFactory.currency(for: .uk)?.code() ?? noCurrencyCode