FileHelper

FileEncodable.swift

struct DataEncodable<T> {
  
  static func encode(var value: T) -> NSData {
    return withUnsafePointer(&value) { NSData(bytes: $0, length: sizeof(T)) }
  }
  
  static func decode(data: NSData) -> T {
    let pointer = UnsafeMutablePointer<T>.alloc(sizeof(T))
    data.getBytes(pointer, length: sizeof(T))
    
    return pointer.move()
  }
}

struct File {
  
  static func save<T>(x: T, toFile file: String) -> Bool {
    let url = FileHelper.filePath(file)
    let data = DataEncodable.encode(x)
    
    return data.writeToFile(url, atomically: true)
  }
  
  static func load<T>(file: String) -> T? {
    let url = FileHelper.filePath(file)
    let data = NSData(contentsOfFile: url)
    
    return data.map { DataEncodable.decode($0) }
  }
}

FileHelper.swift

public class FileHelper {
  
  public static var documentDirectory: String {
    return directoryPath(.DocumentDirectory)
  }
  
  public static func filePath(file :String, directory: NSSearchPathDirectory = .DocumentDirectory) -> String {
    return directoryPath(directory).stringByAppendingPathComponent(file)
  }
  
  //  MARK:- Private
  private static func directoryPath(dir: NSSearchPathDirectory) -> String {
    return NSSearchPathForDirectoriesInDomains(dir, .UserDomainMask, true).first as! String
  }
}

use.playground

struct Cat: Creature {
  let name: String
}

var cat = Cat(name: "A")
let data = File.save(cat, toFile: "A.txt")
let cat1: Cat? = File.load("A.txt")