Fixed errors that pop up when you try to compile the sample code from this tutorial on the latest Xcode(7.3.1): https://www.raywenderlich.com/85528/user-accounts-ios-ruby-rails-swift
Let me know if you have any issue compiling!
Please beware that I didn't bother fixing the warnings since they won't prevent you from compiling and running the app. Also, my fixes might not be optimal since I am quite new to iOS dev and the Swift language.
NOTE
You must specify API Authentication values and Heroku app link string in HTTPHelper.swift file for the app to be operational. Please try following the whole tutorial if you don't know what those values are for.