Embedded Swift Improvements Coming in Swift 6.3

Embedded Swift is a subset of Swift that’s designed for low resource usage, making it capable of running on constrained environments like microcontrollers. Using a special compilation mode, Embedded Swift produces significantly smaller binaries than regular Swift. While a subset of the full language, the vast majority of the Swift language works exactly the same in Embedded Swift. Additional information is described in the Embedded Swift vision document.

Embedded Swift is evolving rapidly. This post describes a number of improvements made in the last few months, covering everything from improved C interoperability to better debugging and steps toward a complete linkage model for Embedded Swift.

→ swift.org/blog/embedded-swift-improvements-coming-in-swift-6.3

Swift 6.3 advances Embedded Swift, a subset for microcontrollers, with key improvements in libraries, diagnostics, C interoperability, debugging, and linking. Floating-point types now support description and debugDescription via a Swift implementation, while new EmbeddedRestrictions warnings flag unavailable constructs like untyped throws.

The Swift MMIO package 0.1.x adds bug fixes, documentation, and svd2swift code generation from SVD files, with SVD2LLDB enhancing register inspection in LLDB. C interoperability gains @c functions and enums for C-compatible declarations, better tolerance for signature mismatches, and @section/@used attributes for linker control.

Debugging improves with value printing, core dump inspection of standard library types like Dictionary, and reliable ARMv7m exception unwinding. Linking progresses with weak symbol definitions to avoid duplicates and @export for controlling function visibility, moving toward a formalized Embedded Swift linkage model.

These features, available in nightly toolchains, enhance safety, performance, and usability on constrained devices.