Swift 3不要用 "+" 运算！！

真不是标题党，除了正常的算数运算，其他的千万要绕着"+"运算远一点啊。

这2天Xcode把我们团队坑瘸了，随着代码越来越多，这编译速度就越来越慢，越来越慢……今天我一个下午一边敲一遍编译，就编译成功了一次，简直是令人发指啊！😢

实在是不能忍了，满世界找了找原因，在stackoverflow上找到这个编译时间查看工具BuildTimeAnalyzer-for-Xcode，再回想起了一个零赞同的我以为是乱写的回答(当时觉得完全不可能才印象深刻)，逐渐开始找到了头绪，项目编译慢的主要原因居然真是因为它说的"+"运算导致的。我靠！

下面是BuildTimeAnalyzer运行图。每一行都是一个swift文件(或某个swift文件的一个closure)的编译时间……项目里的这些文件大多有共同的特征：多个string类型的变量以+运算相连。恩，一个230行代码的文件，也就编译了4分钟而已嘛。

image.png

然后顺藤摸瓜找到了这个讨论http://stackoverflow.com/questions/29707622/bizarre-swift-compiler-error-expression-too-complex-on-a-string-concatenation，Honey的回答大致意思就是说swift3的 "+ " 运算严重超载了，运算时间会呈指数级的增长？？？！！！

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怎么不用+号，大家应该都知道吧，let combinedString = "\(hello) \(world)"就好了。本文还没结束，我发现stackoverflow上其他一些开发者的说法，也一齐转过来了。

比如说Stefan Nestorov说不能这样使用??,会编译慢：

let name = "\(someString ?? "")"

bibscy说Dictionary不能这样写

func toAnyObject() -> AnyObject {
  return
      ["BookingAmount":BookingAmount,
     "BookingNumber":BookingNumber,
     "PostCode":PostCode,
     "SelectedBathRow":SelectedBathRow,
     "SelectedBedRow":SelectedBedRow,
     "DateAndTime":DateAndTime,
     "TimeStampDateAndTime":TimeStampDateAndTime,
     "TimeStampBookingSavedInDB": TimeStampBookingSavedInDB,
     "FrequencyName":FrequencyName,
     "FrequecyAmount":FrequecyAmount,
     "insideCabinets": insideCabinets,
     "insideFridge": insideFridge,
     "insideOven": insideOven,
     "laundryWash": laundryWash,
     "interiorWindows": interiorWindows,
     "FullName":FullName,
     "SuppliesName":SuppliesName,
     "SuppliesAmount":SuppliesAmount,
     "FlatNumber":FlatNumber,
     "StreetAddress":StreetAddress,
     "PhoneNumber":PhoneNumber,
     "EmailAddress":EmailAddress] as AnyObject
}

要这样写：

func toAnyObject() -> AnyObject {

    var someDict = [String : AnyObject]()
    someDict["BookingAmount"] = self.BookingAmount as AnyObject?
    someDict["BookingNumber"] = self.BookingNumber as AnyObject?
    someDict["PostCode"] = self.PostCode as AnyObject?
    someDict["SelectedBathRow"] = self.SelectedBathRow as AnyObject?
    someDict["SelectedBedRow"] = self.SelectedBedRow as AnyObject?
    someDict["DateAndTime"] = self.DateAndTime as AnyObject?
    someDict["TimeStampDateAndTime"] = self.TimeStampDateAndTime as AnyObject?
    someDict["TimeStampBookingSavedInDB"] = self.TimeStampBookingSavedInDB as AnyObject?
    someDict["FrequencyName"] = self.FrequencyName as AnyObject?
    someDict["FrequecyAmount"] = self.FrequecyAmount as AnyObject?
    someDict["insideCabinets"] = self.insideCabinets as AnyObject?
    someDict["insideFridge"] = self.insideFridge as AnyObject?
    someDict["insideOven"] = self.insideOven  as AnyObject?
    someDict["laundryWash"] = self.laundryWash as AnyObject?
    someDict["interiorWindows"] = self.interiorWindows as AnyObject?
    someDict["FullName"] = self.FullName as AnyObject?
    someDict["SuppliesName"] = self.SuppliesName as AnyObject?
    someDict["SuppliesAmount"] = self.SuppliesAmount as AnyObject?
    someDict["FlatNumber"] = self.FlatNumber as AnyObject?
    someDict["StreetAddress"] = self.StreetAddress as AnyObject?
    someDict["PhoneNumber"] = self.PhoneNumber as AnyObject?
    someDict["EmailAddress"] = self.EmailAddress as AnyObject?

    return someDict as AnyObject
}

Ben Simon说Array不要这样写

let array = ["1", "2", "3", "4", "5", "6", "7", "8"]

而要写成这样：

let array: Array<String> = ["1", "2", "3", "4", "5", "6", "7", "8"]

Dylan Gattey说

let combinedArrays = array1 + array2

是不好的，要这样

[array1, array2].joined()

image.png

还让不让人用swift开发了！

所以用Xcode8.3开发swift应用的同学们，如果你发现你的编译速度慢的令人发指，一定要记得你看过本文啊！

Xcode8.3/Swift3简直是谋财害命。10天一新版，都发了3版了，还是这么烂啊！