We’re delighted to announce the general availability of Swift 6. This is a major new release that expands Swift to more platforms and domains. Many people know of Swift as a language for app development, with a million apps on the App Store. But Swift is great for more than just apps. Swift’s safety, speed, and approachability make it a great choice for many other use cases including libraries, internet-scale services, and the most performance-critical and secure code. Swift 6 scales even further through new low-level programming features, an embedded Swift language subset, expanded Linux and Windows support, new cross-platform APIs including the new Swift Testing library, and more. Read on for a deep dive into changes to the language, standard libraries, debugging, platform support, and next steps for getting started with Swift 6.
Language and Standard Library
Concurrency
Swift has long offered memory safety, ensuring that variables are initialized before they’re used, memory isn’t accessed after it’s been deallocated, and array indices are checked for out-of-bounds errors. Swift 6 now includes a new, opt-in language mode that extends Swift’s safety guarantees to prevent data races in concurrent code by diagnosing potential data races in your code as compiler errors. Data-race safety checks were previously available as warnings in Swift 5.10 through the `-strict-concurrency=complete` compiler flag. Thanks to improved Sendable inference and new compiler analysis for transferring mutable state from one actor to another, Swift 6 warnings about data-race safety have fewer false positives. You can find more information about the Swift 6 language mode and how to migrate at Swift.org/migration.
Typed Throws
Swift 6 enables functions to specify the type of error that they throw as part of their signature. This feature is useful in generic code that forwards along errors thrown in client code, or in resource-constrained environments that cannot allocate memory, such as in embedded Swift code. Typed throws generalizes over throwing and non-throwing functions, making error handling more precise and efficient.
Ownership
Swift 5.9 introduced non-copyable types with the `~Copyable` syntax for modeling resources with unique ownership, and writing performance-conscious code by eliminating the runtime overhead associated with copying. Swift 6 now supports these types with the generics system, making it possible to write generic code that works with both copyable and non-copyable types. This feature is particularly beneficial for performance-critical applications.
C++ Interoperability
Swift 5.9 introduced bidirectional interoperability with C++ to seamlessly bring Swift to more existing projects. Swift 6 expands interoperability support to C++ move-only types, virtual methods, default arguments, and more standard library types including `std::map` and `std::optional`. This allows for more efficient and flexible integration between Swift and C++ codebases.
Embedded Swift
Swift 6 includes a preview of Embedded Swift, a language subset and compilation mode suitable for embedded software development, such as programming microcontrollers. The toolchain supports ARM and RISC-V bare-metal targets. Embedded Swift produces small and standalone binaries by relying on generic specialization. This makes it suitable for platforms with tight memory constraints and low-level environments with limited runtime dependencies.
Embedded Swift enables efficient programming for microcontrollers.
Productivity Enhancements
Swift 6 introduces a number of productivity enhancements, including `count(where:)` to streamline counting the number of elements in a sequence that satisfy a predicate, pack iteration for writing natural for-loops over the elements in a value parameter pack, access control for imports, and `@attached(body)` macros for synthesizing and augmenting function implementations.
Debugging
Custom LLDB Summaries with @DebugDescription
Swift 6 provides a new debugging macro to easily customize how an object is displayed in LLDB when using the `p` command, and in the variables view in Xcode and VSCode, by using a formatting scheme that does not run arbitrary code. This allows for more precise and user-friendly debugging experiences.
Custom LLDB summaries enhance the debugging process in Swift.
Libraries
Foundation
Swift 6 unifies the implementation of Foundation across all platforms. The modern, portable Swift implementation provides consistency across platforms, it’s more robust, and it’s open source. Core types like `JSONDecoder`, `URL`, `Calendar`, `FileManager`, `ProcessInfo`, and more have been completely reimplemented in Swift, providing a new level of cross-platform consistency, reliability, and performance.
Swift Testing
Swift 6 introduces Swift Testing, a new testing library designed from the ground up for Swift. It includes expressive APIs that make it easy to write and organize tests. It provides detailed output when a test fails using macros like `#expect`. And it scales to large codebases with features like parameterization to easily repeat a test with different arguments.
Platform Support
Swift is designed to support development and execution on all major operating systems, and platform consistency and expansion underpins Swift’s ability to reach new programming domains. Swift 6 brings major improvements to Linux and Windows across the board, including support for more Linux distributions and Windows architectures.
Fully Static SDK for Linux
Swift 6 supports building fully statically linked executables for Linux; these have no external dependencies, making them ideal for situations where you want to copy a program directly onto a system or into a container and run it without installing any extra software.
Swift 6 enhances support for Linux, making it more versatile for various applications.
Next Steps
You can try out these exciting new developments in Swift 6 today! Install the official Swift 6 toolchains for macOS, Linux, and Windows at Swift.org/install.
Remember these 3 key ideas for your startup:
Enhanced Safety and Performance: Swift 6 introduces new concurrency features and typed throws, enhancing safety and performance. This is crucial for startups developing performance-critical applications.
Cross-Platform Consistency: With unified Foundation implementation and expanded platform support, Swift 6 ensures your applications run consistently across macOS, iOS, Linux, and Windows. This is vital for startups aiming for a broad user base.
Embedded Development: The introduction of Embedded Swift opens new avenues for startups in the IoT and embedded systems space, allowing for efficient and low-overhead development.
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