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) |