Apple has released Swift 6.4, an upgrade to the programming language that brings improvements across the board including core library APIs, builds, debugging, interoperability with other platforms, and performance.
Swift 6.4 was announced September 15. “Swift aims to be a great choice across the stack, from apps and servers to systems code, embedded devices, and the browser. This release deepens that support, and makes everyday code easier to write,” Apple’s Joe Heck and Holly Borla wrote in the announcement. They listed the following highlights of the release:
- Swift Build is now the default in Swift Package Manager, so your projects build the same way on Linux, macOS, and Windows.
- Subprocess reaches 1.0, a stable, cross-platform way to run and interact with other programs from Swift, from command-line tools to streaming processes.
- Interoperability reaches further, with Swift’s Span now bridging directly with C++20’s
std::span, and Swift/Java interop extending its async and callback support. - Swift runs faster in the browser, with WebAssembly bridging through JavaScript kit up to 40 times faster, and the Wasm SDK available directly from Swift.org.
- Embedded Swift grows more capable, with support for existential types and richer error handling for microcontroller-class targets.
- Performance improves while maintaining memory safety, with new array types that hold non-copyable elements without copy-on-write overhead, and the new
Iterableprotocol for iterating without copies.
Swift 6.4 also completes a multi-release overhaul of how the compiler tracks Swift modules in debug info. LLDB now imports modules through precise dependency tracking instead of by-name lookups. Debug builds on Linux and Windows, and dSYM bundles on Darwin, shrink significantly because binary Swift modules are no longer embedded in them. Swift 6.4 also makes it easier to avoid unnecessary copies of data while staying memory-safe, extending earlier work on Span, non-copyable types, and InlineArray, according to the announcement.
