Embedded Swift Gets Major Upgrades in Swift 6.3

Swift 6.3 is bringing significant enhancements to Embedded Swift, the subset of Swift designed for resource-constrained environments like microcontrollers. Here's what's new:

Key Improvements

Libraries & Standard Library

• Floating-point printing: The description and debugDescription properties now work for Float, Double, and other floating-point types with a new all-Swift implementation
• Better diagnostics: New EmbeddedRestrictions diagnostic group warns about unsupported language constructs
• Swift MMIO 0.1.x: Includes code generation from SVD files and improved debugging with SVD2LLDB plugin

C Interoperability

• @c attribute: Define C-compatible functions and enums (from SE-0495)

@c(MyLib_initialize) public func initialize() { ... } 

• Improved type matching: Better tolerance for mismatching C signatures, eliminating cryptic deserialization errors

Debugging

• Enhanced LLDB support: Better value printing for Embedded Swift types
• Core dump inspection: Dictionary, Array, and other common types now inspectable without a live process
• ARMv7m exception unwinding: Complete backtraces through exception frames

Linking & Compilation

• @section and @used attributes: Control where globals are emitted and ensure symbols aren't stripped (SE-0492)
• Weak symbol definitions: Fixes duplicate symbol errors in diamond dependencies
• @export attribute: Better control over function visibility (SE-0497)

Want to dive deeper? Read the full announcement on Swift.org