Since you're doing iOS development, I am going to assume you're using a Mac. If this assumption is correct, whatever you choose to learn, I strongly suggest you

Since you're doing iOS development, I am going to assume you're using a Mac. If this assumption is correct, whatever you choose to learn, I strongly suggest you install Dash (http://kapeli.com/dash http://kapeli.com/dash) and grab all documentation related to your language of choice. HTH!