What’s New in Swift 3?

Improvements to Tooling

Swift is a language, and a large part of writing it involves using a development environment - which for Apple developers is likely Xcode! The changes going on with the tooling will impact how you write Swift every day.

Swift 3 fixes bugs in the compiler and IDE features. It also improves the precision of error and warning messages. And as you might expect, with each release, Swift is getting faster in how it runs and compiles:

• By improving string hashing there was a 3x speedup in dictionaries of strings
• By moving objects from the heap to the stack there was a 24x speedup (in some cases)
• The compiler now caches multiple files at once (when doing whole module optimization)
• Code size optimization has reduced the compiled size of Swift code. Apple's demo Demobots reduced the compiled size to 77% of the original

Xcode is also learning how to think in native Swift:

• When you right-click on an API method like sort() and jump to its definition, you used to be taken to a cryptic header file. Now, in Xcode 8, you see that sort() is an extension to Array like you would expect.
• Swift Snapshots are like the nightly releases of Swift Evolution. They offer a chance to work with the new syntax before its fully baked into Xcode. Xcode 8 can load and run Swift Snapshots in playgrounds.

The Swift Package Manager

Open source Swift is actually a family of repositories including the language, the core libraries, and the package manager. Together, this suite makes up what we think of as Swift. The Swift Package Manager defines a simple directory structure for any Swift code that you share and import into projects.

Similar to package managers you may be used to such as Cocoapods or Carthage, Swift's package manager will download dependencies, compile them, and link them together to create libraries and executables. Swift 3 is the first release to include the Swift Package Manager. There are 1,000 libraries that already support it. The Swift Package Manager is presently mainly used for server code projects and does not yet support iOS projects in Xcode.

Planned Future Features

The core team aimed for Swift 3 to let you keep your code from version to version in the future by striving to avoid breaking changes and offering long deprecation cycles. That goal was nearly reached, but the point releases on the way to Swift 4 will have a few more changes this year.

There were also some loftier, related goals that weren't reached for this release, namely generics additions and Application Binary Interface (ABI) stability.

The generics additions will include recursive protocol constraints and the ability to make a constrained extension conform to a new protocol (i.e., an array of Equatable elements is Equatable). Swift can't declare ABI stability until these features are complete.

ABI stabilization will allow applications and libraries compiled with different versions of Swift to be able to be linked and interact with each other. This is a vital step for third party libraries to ship frameworks without providing the source code. Right now, new versions of Swift not only require them to update their code, but to rebuild their frameworks as well.

Additionally, ABI stability would remove the need to ship the Swift standard library along with binaries, as is currently the case with iOS and macOS apps created with Xcode. Right now binaries are bundled with 2 MB extra filesize that ensures that they will run on future operating systems.

Where to Go From Here?

Swift continues to evolve as the community converges on best practices. While still in its infancy, the language has a lot of momentum and a big future. Swift already runs on Linux, and you will likely see it running on servers in addition to devices in the coming years. Designing a language from scratch certainly has its advantages as opportunities to break ABI stability once it's locked down will be rare. This is a unique chance to get the language correct without regrets.

Swift is also expanding its reach. Apple is eating their own dogfood. Teams at Apple use Swift on the Music app, Console, picture-in-picture in Sierra, the Xcode Documentation viewer, and the new Swift Playgrounds app for iPad.

Speaking of which, there's a big push to get non-programmers learning Swift, both on the iPad and through education initiatives.

The takeaway here is that Swift continues its ascent: the names are better, the code reads clearer, and you have the tools to migrate. If you're inspired to dig deeper, you can watch the WWDC session videos.

There will surely be more to come in the journey to Swift 4. We’ll be staying on top of all the updates here, so keep an eye out for tutorials, book announcements, and videos as we start using the exciting changes.

What parts of Swift 3 are you most excited about? What would you like us to cover? Let us know in the comments below!