Swift 1.2 and Xcode 6.3 beta

Today Swift 1.2 was released as part of Xcode 6.3 beta. This beta release includes a significantly enhanced Swift compiler, as well as new features in the Swift language itself. For the complete list of changes, read the release notes. This blog post will focus on the highlights.

Compiler improvements

The Swift 1.2 compiler was engineered to be more stable and to improve performance in every way. These changes also provide a better experience when working with Swift in Xcode. Some of the most visible improvements include:

  • Incremental builds — Source files that haven’t changed will no longer be re-compiled by default, which will significantly improve build times for most common cases. Larger structural changes to your code may still require multiple files to be rebuilt.
  • Faster executables — Debug builds produce binaries that run considerably faster, and new optimizations deliver even better Release build performance.
  • Better compiler diagnostics — Clearer error and warning messages, along with new Fix-its, make it easier to write proper Swift 1.2 code.
  • Stability improvements — The most common compiler crashes have been fixed. You should also see fewer SourceKit warnings within the Xcode editor.

New language features

In Swift 1.2, the language has been further refined to ensure safe, predictable behavior. We also continue to improve the interaction between Swift and Objective-C. Some of the more notable changes include:

  • as! for failable casts — Casts that can fail at runtime are now expressed with the new as! operator to make their potential for runtime failure clear to readers and maintainers of your code.
  • Nullability may now be expressed in Objective-C headers — New Objective-C extensions in Clang allow you to express the nullability of pointers and blocks in your Objective-C API. You can provide Objective-C frameworks that work great with Swift code, and improve your Swift experience when mixing and matching with Objective-C code in your own project.
  • Swift enums can now be exported to Objective-C using the @objc attribute — For example, the following Swift code:
@objc enum Bear: Int {
	case Black, Grizzly, Polar

imports into Objective-C as:

typedef NS_ENUM(NSInteger, Bear) {
	BearBlack, BearGrizzly, BearPolar
  • let constants are now more powerful and consistent — The new rule is that a let constant must be initialized before use (like a var), and that it may only be initialized, not reassigned or mutated after initialization.

This enables patterns like:

let x : SomeThing
if condition {
	x = foo()
} else {
	x = bar()

This formerly required the use of a var even though there is no mutation taking place. Properties have been folded into this model to simplify their semantics in initializers as well.

  • More powerful optional unwrapping with if let — The if let construct can now unwrap multiple optionals at once, as well as include intervening boolean conditions. This lets you express conditional control flow without unnecessary nesting.
  • New native Set data structure — An unordered collection of unique elements that bridges with NSSet and provides value semantics like Array and Dictionary.


We appreciate all of the bugs you have filed, and expect that many of the most common issues have been fixed in this beta. Swift 1.2 is a major step forward for both the language and the tools. It does include some source-incompatible changes that require updates to your code, so Xcode 6.3 includes a migrator to help automate the process. To begin the migration, click the Edit menu, then choose Convert > To Swift 1.2...

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