Swift - 下标脚本方法介绍及实例

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)