定义下标脚本之后，可以使用“[]”来存取数据类型的值。

示例1：实现一个我们自定的字符串类，可以方便的通过索引获取某一个字符值，或某一部分字符串。同时也可以通过索引，给某一部分赋值。

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class SubString {      var str: String = ""      init (str: String )      {          self .str = str;      }            /**下标脚本：获取/设置部分字符串**/      subscript(start: Int , length: Int ) -> String      {          get {              return (str as NSString ).substringWithRange( NSRange (location: start, length: length))          }          set {              var tmp = Array (str)              str = ""              var s = ""              var e = ""              for (idx, item) in enumerate (tmp) {                  if (idx < start)                  {                      s += "\(item)"                  }                  if (idx >= start + length)                  {                      e += "\(item)"                  }              }              str = s + newValue + e          }      }            /**下标脚本：获取/设置字符**/      subscript(index: Int ) -> String      {          get {              return String ( Array (str)[index])          }          set {              var tmp = Array (str)              tmp[index] = Array (newValue)[0]              str = ""              for (idx, item) in enumerate (tmp) {                  str += "\(item)"              }          }      } }   var str = SubString (str: "hangge.com" ) println (str[7,3])  //获取字符串：com println (str[7])  //获取字符：c   str[7,3] = "COM"  //设置部分字符串 str[0] = "H" //设置部分字符 println (str[0,10])

示例1改进：通过类扩展，也可以直接给String类添加索引功能，代码如下：

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extension String {      subscript(start: Int , length: Int ) -> String          {          get {              return ( self as NSString ).substringWithRange( NSRange (location: start, length: length))          }          set {              var tmp = Array ( self )              var s = ""              var e = ""              for (idx, item) in enumerate (tmp) {                  if (idx < start)                  {                      s += "\(item)"                  }                  if (idx >= start + length)                  {                      e += "\(item)"                  }              }              self = s + newValue + e          }      }      subscript(index: Int ) -> String          {          get {              return String ( Array ( self )[index])          }          set {              var tmp = Array ( self )              tmp[index] = Array (newValue)[0]              self = ""              for (idx, item) in enumerate (tmp) {                  self += "\(item)"              }          }      } }   var str = "hangge.com" println (str[7,3]) println (str[7])   str[7,3] = "COM" str[0] = "H"   println (str[0,10])

示例2：使用一维数组结合下标方法一定程度上模拟实现了二维数组

 

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class Matrix {      let rows: Int , columns: Int      var grid: [ Double ]            init (rows: Int , columns: Int ) {          self .rows = rows          self .columns = columns          grid = Array (count: rows * columns, repeatedValue: 0.0)      }            func indexIsValidForRow(row: Int , column: Int ) -> Bool {          return row >= 0 && row < rows && column >= 0 && column < columns      }            subscript(row: Int , column: Int ) -> Double {          get {              assert(indexIsValidForRow(row, column: column), "Index out of range" )              return grid[(row * columns) + column]          }          set {              assert(indexIsValidForRow(row, column: column), "Index out of range" )              grid[(row * columns) + column] = newValue          }      } }   var value = Matrix (rows: 20,columns: 20) value[10,10] = 20 println (value)