參考

what's new in Swfit 5.0
Demo

Raw strings

SE-0200增加了 # 符號，使得寫字符串更加簡單。

• 在字符串中包含 " 時不必再加 \

  //before
  let rain = "The \"rain\" in \"Spain\" falls mainly on the Spaniards." 
  //after
  let rain = #"The "rain" in "Spain" falls mainly on the Spaniards."#  
  

• 包含 \ 反斜杠也不需要再加轉義符

  // before
  let keypaths = "Swift keypaths such as \\Person.name hold uninvoked references to properties."
  // after
  let keypaths = #"Swift keypaths such as \Person.name hold uninvoked references to properties."#
  

• 由于反斜杠作為字符串中的字符，所以在插入值的時候需要在后面再加個 #

  //before
 let answer = 42
 let dontpanic = "The answer to life, the universe, and everything is \(answer)"
 // after
 let answer = 42
 let dontpanic = #"The answer to life, the universe, and everything is \#(answer)"#

• 當字符串包含 # 時， 前后應用 ## 包裹字符串

  let str = ##"My dog said "woof"#gooddog"##
  

• 用 #""" 開頭 """#結尾 來表示多行字符串

    let multiline = #"""
    The answer to life,
    the universe,
    and everything is \#(answer).
    """#
  

• 由于不用反斜杠轉義 使得正則表達式更加簡潔明了

   //before
   let regex1 = "\\\\[A-Z]+[A-Za-z]+\\.[a-z]+"
  //after
   let regex2 = #"\\[A-Z]+[A-Za-z]+\.[a-z]+"#
  

Handling future enum cases

SE-0192 在枚舉新增加一個 @unknown 修飾 default 分支,這樣使得將來 enum 再增加一個 case 的時候，編譯器會在該枚舉的switch 代碼里生成一個警告
比如

    enum PasswordError: Error {
          case short
          case obvious
          case simple
    }

    func showOld(error: PasswordError){
             switch error {
             case .short:
                      print("Your password was too short.")
             case .obvious:
                      print("Your password was too obvious.")
             default:
                      print("Your password was too simple.")
             }
    }

上面代碼假如我們再加個 case old,執(zhí)行代碼時它會自動進入到default分支，可這并不是我們想要的結果，因為這個密碼是一個舊密碼而不是密碼太簡單，這時候可以用 @unknown，如下

  enum PasswordError: Error {
            case short
            case obvious
            case simple
            case old
   }

   func showNew(error: PasswordError) {
        switch error {
        case .short:
            print("Your password was too short.")
        case .obvious:
            print("Your password was too obvious.")
        @unknown default:
            print("Your password wasn't suitable.")
        }
    }

這時會產生一個警告 ,因為新增了case old ，switch沒有明確地處理每一個分支。

Checking for integer muliples

SE-0225 integers 新增加了一個 isMultiple(of:) 方法
來檢測一個數(shù)是否是另一個數(shù)的倍數(shù)

  let rowNumber = 4

  /*相當于 if rowNumber %  2 == 0
     改成方法調用更易懂，更方便調用（有代碼補全）
 */
  if rowNumber.isMultiple(of:2) {
      print("Even")
  } else {
      print("Odd")
  }

Counting matching items in a sequence

SE-0220
Sequence 新增加了一個方法 count(where:) 相當于 filter() + count 的結果，但是它更加簡潔一步到位

//before
let scores = [100,80,85]
let passCount = scores.filter{($0 >= 85)}.count

//after 避免生成一個數(shù)組
let scores = [100,80,85]
let passCount = scores.count { $0 >= 85}

這個方法適用于遵循了 Sequence 的所有類型，所以也可以用在 集合 和 字典里。

Transforming and unwrapping dictionary values with compactMapValues()

SE-0218 為字典新增了一個方法 compactMapValues(),正如數(shù)組的compactMap函數(shù)一樣，可以過濾nil,類型轉換

    let times = [
        "Hudson": "38",
        "Clarke": "42",
        "Robinson": "35",
        "Hartis": "DNF"
    ]
    //通過compactMapValues 將值轉換成integer類型，并且將DNF過濾掉
     let finishers1 = times.compactMapValues { Int($0) }
    //也可以這樣寫
     let finishers2 = times.compactMapValues(Int.init)
  
     // 過濾nil
     let people = [
        "Paul": 38,
        "Sophie": 8,
        "Charlotte": 5,
        "William": nil
      ]
     let knownAges = people.compactMapValues { $0 }

結尾

Swift的每次更新都使得寫起代碼越來越簡單高效。
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