Swift Programming Language

About Swift

Swift is a fantastic way to write software, whether it’s for phones, desktops, servers, or anything else that runs code. It’s a safe, fast, and interactive programming language that combines the best in modern language thinking with wisdom from the wider Apple engineering culture and the diverse contributions from its open-source community. The compiler is optimized for performance and the language is optimized for development, without compromising on either.

Swift is friendly to new programmers. It’s an industrial-quality programming language that’s as expressive and enjoyable as a scripting language. Writing Swift code in a playground lets you experiment with code and see the results immediately, without the overhead of building and running an app.

Swift defines away large classes of common programming errors by adopting modern programming patterns:

• Variables are always initialized before use.
• Array indices are checked for out-of-bounds errors.
• Integers are checked for overflow.
• Optionals ensure that nil values are handled explicitly.
• Memory is managed automatically.
• Error handling allows controlled recovery from unexpected failures.

Swift code is compiled and optimized to get the most out of modern hardware. The syntax and standard library have been designed based on the guiding principle that the obvious way to write your code should also perform the best. Its combination of safety and speed make Swift an excellent choice for everything from “Hello, world!” to an entire operating system.

Swift combines powerful type inference and pattern matching with a modern, lightweight syntax, allowing complex ideas to be expressed in a clear and concise manner. As a result, code is not just easier to write, but easier to read and maintain as well.

Swift has been years in the making, and it continues to evolve with new features and capabilities. Our goals for Swift are ambitious. We can’t wait to see what you create with it. 

Version Compatibility

This book describes Swift 4.0.3, the default version of Swift that’s included in Xcode 9.2. You can use Xcode 9.2 to build targets that are written in either Swift 4 or Swift 3.

When you use Xcode 9.2 to build Swift 3 code, most of the new Swift 4 functionality is available. That said, the following features are available only to Swift 4 code:

• Substring operations return an instance of the Substring type, instead of String.
• The @objc attribute is implicitly added in fewer places.
• Extensions to a type in the same file can access that type’s private members.

A target written in Swift 4 can depend on a target that’s written in Swift 3, and vice versa. This means, if you have a large project that’s divided into multiple frameworks, you can migrate your code from Swift 3 to Swift 4 one framework at a time. 

Features

Swift is an alternative to the Objective-C language that employs modern programming-language theory concepts and strives to present a simpler syntax. During its introduction, it was described simply as "Objective-C without the C".
By default, Swift does not expose pointers and other unsafe accessors, in contrast to Objective-C, which uses pointers pervasively to refer to object instances. Also, Objective-C's use of a Smalltalk-like syntax for making method calls has been replaced with a dot-notation style and namespace system more familiar to programmers from other common object-oriented (OO) languages like Java or C#. Swift introduces true named parameters and retains key Objective-C concepts, including protocols, closures and categories, often replacing former syntax with cleaner versions and allowing these concepts to be applied to other language structures, like enumerated types (enums)

Syntactic sugar

Under the Cocoa and Cocoa Touch environments, many common classes were part of the Foundation Kit library. This included the NSString string library (using Unicode), the NSArray and NSDictionary collection classes, and others. Objective-C provided various bits of syntactic sugar to allow some of these objects to be created on-the-fly within the language, but once created, the objects were manipulated with object calls. For instance, in Objective-C concatenating two NSStrings required method calls similar to this:

NSString *str = @"hello,";
str = [str stringByAppendingString:@" world"];

Development and other implementations

Since the language is open-source, there are prospects of it being ported to the web. Some web frameworks have already been developed, such as IBM's Kitura, Perfect and Vapor.
An official "Server APIs" work group has also been started by Apple, with members of the Swift developer community playing a central role.
A second free implementation of Swift that targets Cocoa, Microsoft's Common Language Infrastructure (.NET), and the Java and Android platform exists as part of the Elements Compiler from RemObjects Software.

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