請參考本博客另一篇技術博文：《[Swift]字符串(String類、NSString類)常用操作》

  1 extension String {
  2     
  3     //獲取字符串首字符
  4     var first: String 
  5     {
  6         get
  7         {
  8             return String(self[startIndex])
  9         } 
 10     }
 11     
 12     // 獲取字符串最後一個字符
 13     var last: String 
 
 14     {      
 15         get 
 16         {
 17             let index = self.index(before: self.endIndex)
 18             return String(self[index ])
 19         } 
 20     }
 21     
 22     // 將16進制字符串轉為Int
 23     var hexInt:Int 
 24     {
 25         get 
 26         {
 27             return
 
 Int(self, radix: 16) ?? 0
 28         }
 29     }
 30     
 31     //獲取指定索引位置的字符，返回為字符串形式
 32     func charAt(_ num:Int) -> String
 33     {
 34         guard num < self.count else {
 35             assertionFailure("Index out of range!")
 36             return String()
 37         }
 38
 
         let index = slef.index(str.startIndex,offsetBy: num)
 39         return String(self[index])
 40     }
 41     
 42     //獲取指定索引位置字符的ASCII整數值
 43     func toInt(_ num:Int) -> String
 44     {
 45         guard num < self.count else {
 46             assertionFailure("Index out of range!")
 47             return String()
 48         }
 49         var number:Int = Int()  
 50         for scalar in charAt(num).unicodeScalars  
 51         {  
 52             number = Int(scalar.value)  
 53         }  
 54         return number  
 55     }
 56     
 57     //獲取重復指定次數的字符串
 58     func repeat(_ times: Int ) -> String
 59     {
 60         var result = String()
 61         for i in 0..times {
 62             result += self
 63         }
 64         return result 
 65     }
 66     
 67     //整體反轉字符串
 68     func reverse() -> String
 69     {
 70         return String(slef.reversed())
 71     }
 72 
 73     // 截取字符串：從起始處到index
 74     // - Parameter index: 結束索引
 75     // - Returns: 子字符串
 76     func subStringTo(_ index: Int) -> String {
 77         guard index < self.count else {
 78             assertionFailure("Index out of range!")
 79             return String()
 80         }
 81         let index = self.index(self.startIndex, offsetBy: index)
 82         return String(self[startIndex...index])
 83     }
 84     
 85     // 截取字符串：從index到結束處
 86     // - Parameter index: 開始索引
 87     // - Returns: 子字符串
 88     func subStringFrom(_ index: Int) -> String {
 89         
 90         guard index < self.count else {
 91             assertionFailure("Index out of range!")
 92             return String()
 93         }
 94         guard index >= 0 else {
 95             assertionFailure("index can‘t be lower than 0")
 96             return ""
 97         }
 98         let index = self.index(self.endIndex, offsetBy: index - self.count)
 99         
100         return String(self[index..<endIndex])
101     }
102     
103     // 截取字符串：指定區間
104     // - Parameter range: 閉區間
105     // - Returns: 子字符串
106     func subString(_ range: CountableClosedRange<Int>) -> String {
107         
108         guard range.lowerBound >= 0 else {
109             assertionFailure("lowerBound of the Range can‘t be lower than 0")
110             return String()
111         }
112         guard range.upperBound < self.count else {
113             assertionFailure("upperBound of the Range beyound the length of the string")
114             return String()
115         }
116         let start = self.index(self.startIndex, offsetBy: range.lowerBound)
117         let end = self.index(self.startIndex, offsetBy: range.upperBound + 1)   
118         return String(self[start..<end])
119     }
120     
121     // 隱藏手機號中間字符
122     mutating func hidePhoneNum() {
123         if self.count != 11 {
124             return ;
125         }
126         let start = self.index(self.startIndex, offsetBy: 3)
127         let end = self.index(self.endIndex, offsetBy: -4) 
128         let range = Range.init(uncheckedBounds: (lower: start, upper: end))
129         self.replaceSubrange(range, with: "****")
130     }
131     
132     //使用正則表達式替換
133     func pregReplace(pattern: String, with: String,options: NSRegularExpression.Options = []) -> String {
134         let regex = try! NSRegularExpression(pattern: pattern, options: options)
135         return regex.stringByReplacingMatches(in: self, 
136                               options: [],
137                                 range:NSMakeRange(0, self.count),
138                            withTemplate: with)
139     }
140 }

[Swift]擴展String類：extension String