The Swift standard library defines a base layer of functionality for writing Swift applications. Everything we have used so far in this book is from the Swift standard library. The library defines the fundamental data types, such as the String, Int, and Double types. It also defines collections, optional, global functions, and all the protocols that these types conform to.
One of the best sites to see everything that makes up the standard library is http://swiftdoc.org. This site lists all the types, protocols, operators, and globals that make up the standard library and contains documentation for all of it.
Let's look at how protocols are used in the standard library by looking at the documentation. When you first visit the home page, you will be greeted with a searchable list of everything that makes up the standard library. There is also a...