Swift语言的类扩展是一个强大的工具,我们可以通过类扩展完成如下事情:
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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:给Double增加mm,cm等方法,进行进制转换
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extension Double
{ func mm()-> String
{
return "\(self/1)mm"
}
func cm()-> String
{
return "\(self/10)cm"
}
func dm()-> String {
return "\(self/100)dm"
}
func m()-> String
{
return "\(self/1000)m"
}
func km()-> String
{
return "\(self/(1000*1000))km"
}
} var value = 2000000000.0
println (value.mm())
println (value.cm())
println (value.dm())
println (value.m())
println (value.km())
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