It’s also for those coming from other languages such as Java or C++ who want to bring their knowledge of Swift to the same level as that of their “go-to” language. This book targets experienced (though not necessarily expert) programmers, such as existing Apple-platform developers. Being familiar with the material presented is probably necessary, if not sufficient, for calling yourself an advanced Swift programmer. Hopefully, once you’ve read our book, you’ll have gone from being aware of the basics of the language to knowing about many advanced features and having a much better understanding of how Swift works. We intend to answer many of the “How do I do this?” or “Why does Swift behave like that?” questions we’ve seen come up again and again. Learning more about these features is what this book is about. But after a while, we think you’ll find it necessary to know about these things - whether to improve your code’s performance, or to make it more elegant or expressive, or just to get certain things done. You can certainly use Swift without ever calling into a C library or writing your own collection type. You can get up and running developing apps in Swift without needing to know about generics or overloading or how copy-on-write works under the hood. Swift is a complex language - most programming languages are. The example below iterates over the items in the things array and queries the type of each item with a switch statement.Advanced Swift is quite a bold title for a book, so perhaps we should start with what we mean by it. To discover the specific type of a constant or variable that is known only to be of type Any or AnyObject, you can use an is or as pattern in a switch statement’s cases.
#DOWNCAST ONLY UNWRAPS OPTIONALS MOVIE#
The things array contains two Int values, two Double values, a String value, a tuple of type (Double, Double), the movie “Ghostbusters”, and a closure expression that takes a String value and returns another String value. init ( name : String, director : String ) ).The second subclass, Song, adds an artist property and initializer on top of the base class: It adds a director property on top of the base MediaItem class, with a corresponding initializer. The first subclass, Movie, encapsulates additional information about a movie or film. The next snippet defines two subclasses of MediaItem. (It is assumed that all media items, including all movies and songs, will have a name.) Specifically, it declares a name property of type String, and an init name initializer. This class provides basic functionality for any kind of item that appears in a digital media library. The first snippet defines a new base class called MediaItem.
#DOWNCAST ONLY UNWRAPS OPTIONALS CODE#
The three code snippets below define a hierarchy of classes and an array containing instances of those classes, for use in an example of type casting. You can use type casting with a hierarchy of classes and subclasses to check the type of a particular class instance and to cast that instance to another class within the same hierarchy. Defining a Class Hierarchy for Type Casting You can also use type casting to check whether a type conforms to a protocol, as described in Checking for Protocol Conformance. These two operators provide a simple and expressive way to check the type of a value or cast a value to a different type. Type casting in Swift is implemented with the is and as operators. Type casting is a way to check the type of an instance, or to treat that instance as a different superclass or subclass from somewhere else in its own class hierarchy.
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