Bundle and NS prefix syntax

This has a bit of background to it and it would help a lot if you knew Objective-C, but I'll try to explain it.

Some of the frameworks you use to develop iOS apps have existed for a long time (since since the 1980s), long before Swift was created. In particular, I'm gonna talk about Foundation, which is easily in the top 2 most commonly used frameworks on iOS. You can still use all of them in Swift, but like all of Apple's frameworks, Foundation is written in Objective-C. In fact, Foundation was written to act sort of as Objective-C's standard library. Objective-C didn't always have the concept of modules like Swift does now. Nowadays in Swift, if I make a library that you wanna use that has a class/struct/enum/protocol that's named the same as one of your classes/structs/enums/protocols, it's easy to disambiguate, like this:

import MyFramework

let mine = MyFramework.SomeObject()
let yours = YourApp.SomeObject() // This is an entirely different class/struct/enum/protocol than the one above

In Objective-C this was/is impossible. When you imported another framework, all of its symbols were effectively pasted into your app, so if you named something the same as in a framework you're using, it'd cause a compiler error. Objective-C's solution at the time was to have every developer add a "class prefix" to their classes. Instead of naming my class SomeObject, I'd name it MFSomeObject, and you'd name yours YASomeObject. That way, their names would be different, and it wouldn't cause a compiler error. A class prefix is (usually) 2 capital letters that you put at the beginning of your class name, and those 2 letters are usually your initials or your project's initials. My name is Michael Hulet, so I usually use MH, but I'm working on an app right now called DinnerRoll, so I might use DR in that project. Objective-C and the Foundation framework were written by a company called NeXT (which was bought by Apple in the '90s), and their popular operating system was called NeXTSTEP, so the class prefix they used in Foundation was NS.

The developers of Swift decided that since Swift has modules, it doesn't look very good in Swift to have class prefixes in front of every symbol. They've recommended from the start to not use class prefixes, but in Swift 3, they took it so far as to want to remove the NS prefix from all of Foundation's symbols. They decided that rewriting Foundation from scratch in Swift would be an unreasonably insane amount of work, so they made the Swift compiler understand what was going on and had it understand that when you write Notification (or something like that), you actually want to be using the NSNotification class. Thus, in Swift 3, you must write it like that, and it won't recognize the NSNotification symbol anymore.