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：comprintln(str[7]) //获取字符：cstr[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] = 20println(value) |