http://d.hatena.ne.jp/shunsuk/20091008/1255003166

http://d.hatena.ne.jp/ogakky/20110711/1310349297

http://qiita.com/emadurandal/items/04c11db5eb1117eabe1e http://crunchtimer.jp/blog/technology/swift/3244/

http://qiita.com/uskiita/items/c643f5868f60b496911e

http://qiita.com/ironsand/items/6c301fef730d53f35bc3

http://d.hatena.ne.jp/naokibtn/20130217/1361120970

http://akiyoko.hatenablog.jp/entry/2014/02/25/003513