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])
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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])
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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)
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