https://medium.com/1205hsiao/clean-code-%E6%8A%80%E8%A1%93%E7%AD%86%E8%A8%9804-%E7%A8%8B%E5%BC%8F%E5%8F%AF%E8%AE%80%E6%80%A7-code-readability-883b422b92de
