This content was released on Dec 15 2017. The official support period is 6-months from this date.
In previous versions of Swift, Objective-C inference was automatic, but now with Swift 4, we have to opt into it. This screencast will show you the ropes.
This is a companion discussion topic for the original entry at https://www.kodeco.com/4374-what-s-new-in-swift-4/lessons/3