作者:Natasha The Robot,原文链接,原文日期:2016-05-27
译者:Crystal Sun;校对:Cee;定稿:Channe

正如上个月在几个会议上我所讲的那样《重构与模式》 这本书被多次提及,特别是在我喜欢的研讨会上。最终我还是读了一小部分(至少是在 WWDC 大会发布后的疯狂情绪高涨之前),并且我希望能够通过将书中的模式(pattern)记录下来,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,并且里面有一些不同的初始化构造器(initializer)。在这个例子中,每个初始化构造器都有存在的理由——每个初始化构造器代表了对应了不同的借款类型:

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。当然了,一些刚刚接触这代码的新人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,甚至会对这些初始化构造器的作用意图感到疑惑。

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的 model 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,而且有时在 Swift 中可以根据不同的实际情况使用更好的方法来解决问题(比如使用枚举)。不过如果我想让我的代码更具可读性、变得更加简洁,我一定会考虑重构成这种模式。

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文章目录
  1. 1. 重构之前
  2. 2. 重构之后