Playgrounds and REPL in Xcode
Much like Swift Playgrounds for iPad, playgrounds in Xcode make writing Swift code incredibly simple and fun. Type a line of code and the result appears immediately. You can then Quick Look the result from the side of your code, or pin that result directly below. The result view can display graphics, lists of results, or graphs of a value over time. You can open the Timeline Assistant to watch a complex view evolve and animate, great for experimenting with new UI code, or to play an animated SpriteKit scene as you code it. When you’ve perfected your code in the playground, simply move that code into your project.
Read-Eval-Print-Loop (REPL). The LLDB debugging console in Xcode includes an interactive version of the Swift language built right in. Use Swift syntax to evaluate and interact with your running app, or write new code to see how it works in a script-like environment. Available from within the Xcode console or in Terminal.
Fast and Powerful
From its earliest conception, Swift was built to be fast. Using the incredibly high-performance LLVM compiler, Swift code is transformed into optimized native code that gets the most out of modern hardware. The syntax and standard library have also been tuned to make the most obvious way to write your code also perform the best.
Swift is a successor to both the C and Objective-C languages. It includes low-level primitives such as types, flow control, and operators. It also provides object-oriented features such as classes, protocols, and generics, giving Cocoa and Cocoa Touch developers the performance and power they demand.
Designed for Safety
Swift eliminates entire classes of unsafe code. Variables are always initialized before use, arrays and integers are checked for overflow, and memory is managed automatically. Syntax is tuned to make it easy to define your intent — for example, simple three-character keywords define a variable ( var ) or constant ( let ).
Another safety feature is that by default Swift objects can never be nil. In fact, the Swift compiler will stop you from trying to make or use a nil object with a compile-time error. This makes writing code much cleaner and safer, and prevents a huge category of runtime crashes in your apps. However, there are cases where nil is valid and appropriate. For these situations Swift has an innovative feature known as optionals. An optional may contain nil, but Swift syntax forces you to safely deal with it using the ? syntax to indicate to the compiler you understand the behavior and will handle it safely.
You can create an entirely new application with Swift today, or begin using Swift code to implement new features and functionality in your app. Swift code co-exists along side your existing Objective-C files in the same project, with full access to your Objective-C API, making it easy to adopt.
To get started with Swift, download Xcode and follow the tutorials available on the Resources tab.