重构：创建方法

原文链接： https://www.natashatherobot.com/refactoring-to-creation-method/
作者： Natasha The Robot
原文日期： 2016-05-27
译者： Crystal Sun

我上个月参加了几次会议并发表演讲，Refactoring to Patterns 这本书被多次提及，特别是在我喜欢的研讨会上，出现多次。我最终还是没太有时间读（至少是在 WWDC 大会发布后的疯狂情绪高涨之前），我想先存档我喜欢的模式以供将来参考。我还发现，通过把书中的 Java 代码翻译成 Swift，我能更好地记住这些知识点。

第一个模式就是创建方法。

重构之前

先假设你有一个 model，比如是借款，model 里有一堆不同的初始化构造器（initializer）。在这个例子中，每个初始化构造器（initializer）都有自己存在的原因，并且对应这不同的借款类型：

struct Loan {
    let commitment: NSDecimalNumber
    let riskRating: Float
    let maturity: Int
    let expiry: NSDate?
    let capitalStrategy: String?
    let outstanding: NSDecimalNumber?
    
    init(commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate?, capitalStrategy: String?, outstanding: NSDecimalNumber?) {
        self.commitment = commitment
        self.riskRating = riskRating
        self.maturity = maturity
        self.expiry = expiry
        self.capitalStrategy = capitalStrategy
        self.outstanding = outstanding
    }
    
    init(commitment: NSDecimalNumber, riskRating: Float, maturity: Int) {
        self.init(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: nil, capitalStrategy: nil, outstanding: nil)
    }
    
    init(commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) {
        self.init(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: nil, outstanding: nil)
    }
    
    init(commitment: NSDecimalNumber, outstanding: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) {
        self.init(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: nil, outstanding: outstanding)
    }
    
    init(capitalStrategy: String, commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) {
        self.init(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: capitalStrategy, outstanding: nil)
    }
    
    init(capitalStrategy: String, commitment: NSDecimalNumber, outstanding: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) {
        self.init(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: capitalStrategy, outstanding: outstanding)
    }
}

看看这代码，你会完全没有思路（除非你知道所有的借贷类型），不知道该用哪个初始化构造器（initializer）。当然了，一些新人刚刚接触这代码的时候可能还对项目的业务不是很清楚，所以他们可能会用错初始化构造器（initializer），甚至会困惑这些初始化构造器（initializer）的作用意图。

是时候来重构了！

重构之后

用创建方法（Creator Method）重构后的代码如下：

struct Loan {
    let commitment: NSDecimalNumber
    let riskRating: Float
    let maturity: Int
    let expiry: NSDate?
    let capitalStrategy: String?
    let outstanding: NSDecimalNumber?
    
     // 原来的初始化构造器（initializer）现在现在可以是私有的
    private init(commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate?, capitalStrategy: String?, outstanding: NSDecimalNumber?) {
        self.commitment = commitment
        self.riskRating = riskRating
        self.maturity = maturity
        self.expiry = expiry
        self.capitalStrategy = capitalStrategy
        self.outstanding = outstanding
    }
    
    static func createTermLoan(commitment: NSDecimalNumber, riskRating: Float, maturity: Int) -> Loan {
        return Loan(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: nil, capitalStrategy: nil, outstanding: nil)
    }
    
    static func createTermLoan(capitalStrategy: String, commitment: NSDecimalNumber, outstanding: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) -> Loan {
        return Loan(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: capitalStrategy, outstanding: outstanding)
    }
    
    static func createRevolverLoan(commitment: NSDecimalNumber, outstanding: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) -> Loan {
        return Loan(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: nil, outstanding: outstanding)
    }
    
    static func createRevolverLoan(capitalStrategy: String, commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) -> Loan {
        return Loan(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: capitalStrategy, outstanding: nil)
    }
    
    static func createRCTL(commitment: NSDecimalNumber, riskRating: Float, maturity: Int, expiry: NSDate) -> Loan {
        return Loan(commitment: commitment, riskRating: riskRating, maturity: maturity, expiry: expiry, capitalStrategy: nil, outstanding: nil)
    }
}

注意到重构后的代码多么漂亮了吗！当你初始化一个借贷时，你知道它的作用了。

虽然我一般不会在类里使用这么多的初始化构造器（initializer），根据不同的实际情况，设置可能还有更好的方法（比如：枚举），但我一定会考虑重构成这种模式，让我的代码更具可读性，更加简洁。

本文由 SwiftGG 翻译组翻译，已经获得作者翻译授权。