read write from files in swift

rw.swift

let fileMgr = NSFileManager.defaultManager()
  func saveToFile(str: String, file: String) {
    var path = NSHomeDirectory().stringByAppendingPathComponent
("Documents").stringByAppendingPathComponent(file)
Note Each app can write only to certain a certain folder inside the application home (for example, the Documents folder). The most common error is probably trying to create a file in the wrong place.
var data = str.dataUsingEncoding(NSUTF8StringEncoding)
    var ok = fileMgr.createFileAtPath(path, contents: data, attributes: nil)
  }
  func retrieveFromFile(file: String) -> String? {
    var path = NSHomeDirectory().stringByAppendingPathComponent
    ("Documents").stringByAppendingPathComponent(file)
    if let data = fileMgr.contentsAtPath(path) {
      return NSString(data:data, encoding: NSUTF8StringEncoding)
    }
return nil }
  func deleteFile(file: String) {
    var path = NSHomeDirectory().stringByAppendingPathComponent
    ("Documents").stringByAppendingPathComponent(file)
    var ok = fileMgr.removeItemAtPath(path, error: nil)
}