swift 字符串的扩展

//调用的地方
func test() -> String {
let str = "1223"
let returnStr = str.document()
return returnStr
}
//写一个扩展
extension String {
/// 沙盒路径之document
func document() -> String {
let documentPath = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true).last!
return (documentPath as NSString).appendingPathComponent((self as NSString).pathComponents.last!)
}

/// 沙盒路径之cachePath
func cache() -> String {
    let cachePath = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.cachesDirectory, FileManager.SearchPathDomainMask.userDomainMask, true).last!
    return (cachePath as NSString).appendingPathComponent((self as NSString).pathComponents.last!)
}

/// 沙盒路径之temp
func temp() -> String {
    let tempPath = NSTemporaryDirectory()
    return (tempPath as NSString).appendingPathComponent((self as NSString).pathComponents.last!)
}

}