Swift 4.0 Released!

Swift 4 is now officially released! Swift 4 builds on the strengths of Swift 3, delivering greater robustness and stability, providing source code compatibility with Swift 3, making improvements to the standard library, and adding features like archival and serialization.

→ swift.org/blog/swift-4.0-released/

Apple released Swift 4 as a major update that builds on Swift 3 with better robustness, stability, source compatibility, standard library improvements, and new features like archival and serialisation.

Key language changes include a faster String implementation with substring support and multi-line literals, collection enhancements such as generic subscripts and one-sided ranges, and archival for structs and enums with type-safe serialisation to formats like JSON.

The compiler supports Swift 3.2 mode for most existing code without changes and Swift 4.0 mode for all new features, allowing gradual migration. The Swift Package Manager gained workflow improvements, a clearer API, and better control over builds and dependencies.