Firstly, I can give you the technical answer, as published by Apple:

Swift is a new programming language for iOS, OS X, watchOS, and tvOS apps that builds on the best of C and Objective-C, without the constraints of C compatibility. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more fun. Swift’s clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to reimagine how software development works. Swift has been years in the making. Apple laid the foundation for Swift by advancing our existing compiler, debugger, and framework infrastructure. We simplified memory management with Automatic Reference Counting (ARC). Our framework stack, built on the solid base of Foundation and Cocoa, has been modernized and standardized throughout. Objective-C itself has evolved to support blocks, collection literals, and modules, enabling framework adoption of modern language technologies without disruption. Thanks to this groundwork, we can now introduce a new language for the future of Apple software development.”

Excerpt From: Apple Inc. “The Swift Programming Language (Swift 2.1).”

Now I can give you my opinion:

  • Swift makes for code that is easier & faster to write.
  • Swift makes for code that is easier & cleaner to read (much more important than ease of writing).
  • Swift code is safer code.
  • Swift breaks free from the out-dated conventions of C-based languages.

When Apple announced Swift at WWDC 2105, I was astounded. That such a major event could have been kept completely secret was amazing. Then I watched every video from WWDC 2015 that discussed Swift. Some were beyond me and others I absorbed. Looking back, I can see that the development of Objective-C over the past few years was all aimed at getting to this point, especially with the introduction of ARC and blocks.

At that time, I was deeply involved in an existing Objective-C project and not able to do much in Swift. But I went through the introduction at the start of the Swift Programming Language book in iBooks and was able to get some ideas about how the language worked.

Some months later, I was able to spend time on Swift. As a learning exercise, I converted an existing Objective-C iOS app to Swift. As might be expected, I really just wrote Objective-C code using Swift syntax. It took a lot more learning before I was able to write Swift-y code instead of just translated Objective-C. In future posts of this series, I hope to enable others to cross that divide faster than I did.

Now when I go back to an Objective-C app, I feel like I am walking a tight-rope. When I use an NSArray, NSSet or NSDictionary, I think “How can I tell what sort of objects are in that array?”. When I use an object, I think “What if that object is nil?”. All of a sudden, code that appeared stable now feels random.

One of the big things that people have latched onto with Swift is that it allows functional programming. I plan several detailed posts on functional programming in this series. But for now I would just recommend that you not worry about the distinction between procedural & functional programming. Both have their advocates and their detractors. Both have their advantages and disadvantages. Just do what ever works for you and we can worry about this later.