{"id":52395,"date":"2026-06-24T16:54:42","date_gmt":"2026-06-24T20:54:42","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=52395"},"modified":"2026-06-24T16:56:49","modified_gmt":"2026-06-24T20:56:49","slug":"swift-6-4","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2026\/06\/24\/swift-6-4\/","title":{"rendered":"Swift 6.4"},"content":{"rendered":"

Swift 6.4 is now available in beta form with Xcode 27. The Swift Evolution proposals are listed here<\/a>.<\/p>\n\n

What’s new in Swift<\/a>:<\/p>\n

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Discover the latest language advancements, including updates for everyday ergonomics, improved concurrency, and safer high-performance code. Explore workflow and language interoperability improvements and updates in embedded Swift.<\/p>\n<\/blockquote>\n\n

Build real-time apps and services with gRPC and Swift<\/a>:<\/p>\n

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Build engaging live experiences with gRPC in your Swift app and backend. gRPC is an open-source RPC framework designed for high-performance, bidirectional streaming APIs. Explore how the gRPC Swift package provides a modern, safe runtime built with Swift concurrency.<\/p>\n<\/blockquote>\n\n

Explore numerical computing in Swift with MLX<\/a>:<\/p>\n

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Bring NumPy-style computing natively to Swift with MLX Swift. Discover how to eliminate cross-language friction in your machine learning workflows by handling image processing, tensor operations, and neural network training in a single, type-safe environment. Explore the APIs that let you leverage GPU acceleration while enjoying the compiler, tooling, and debugging experience you already know.<\/p>\n<\/blockquote>\n\n

Swift Group Lab<\/a>:<\/p>\n

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Join us online for a deep dive into WWDC26 with Apple engineers and designers to ask questions, get advice, and follow the discussion about the week’s biggest Swift announcements.<\/p>\n<\/blockquote>\n\n

Matt Massicotte<\/a>:<\/p>\n

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There’s a voting system. And that means a number of questions weren’t selected. This time I copied those down and I thought it could be fun to take a shot at answering the ones that are more in my area.<\/p>\n<\/blockquote>\n\n

Xcode 27 Beta 2 Release Notes<\/a>:<\/p>\n

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The Swift dependency scanner has been optimized to avoid redundant setup work and header searches when looking up Clang modules during a single dependency-scan action, substantially improving scanning performance.<\/p>\n

As a consequence of this change, every Clang module reachable from a single Swift dependency-scan action must have a unique module name. If two module maps visible to the same scan declare a Clang module with the same name, the scan may report an error.<\/p>\n

[…]<\/p>\n

System now provides Swift APIs for the C stat<\/code>, lstat<\/code>, fstat<\/code>, and fstatat<\/code> system calls. This includes a new Stat<\/code> type with initializers from FilePath<\/code>, FileDescriptor<\/code>, or a C string; FilePath.stat()<\/code> and FileDescriptor.stat()<\/code> instance methods; and supporting types (FileType<\/code>, FileMode<\/code>, FileFlags<\/code>, UserID<\/code>, GroupID<\/code>, DeviceID<\/code>, and Inode<\/code>).<\/p>\n<\/blockquote>\n\n

Wade Tregaskis<\/a>:<\/p>\n

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The final piece of the Prospective Vision for Accessors<\/a>, this allows for more efficient accessors on struct<\/code>s, in a nutshell.<\/p>\n

[…]<\/p>\n

Now there’s a safer version of the existing withUnsafeTemporaryAllocation<\/a><\/code> (first introduced in Swift 5.6<\/a>). It works just like you’d expect. It comes in both “raw bytes” and typed elements versions, just like its unsafe predecessor.<\/p>\n

[…]<\/p>\n

The new isTriviallyIdentical(to:)<\/code> method offers a guaranteed-fast way to check two objects for equality. It is essentially an optimised version of the existing equality condition provided by Equatable<\/code> and the ==<\/code> operator. It’s useful because it guarantees<\/em> O(1) time complexity, whereas ==<\/code> makes no formal guarantees at all (and for many types is O(N) or worse). But unlike the existing identity<\/em> comparison operator ===<\/code> – also O(1) – it promises to do more than just tell if two objects are the exact same pointer, and<\/em> it works on value types (not just reference types).<\/p>\n

[…]<\/p>\n

These<\/a> new types generalise the existing patterns of borrowed and mutable references, that have previously existed in Swift in much more restricted forms (e.g. inout<\/code> parameters are essentially MutableRef<\/code> parameters, and Span<\/code> & MutableSpan<\/code> are array equivalents).<\/p>\n

There’s now a built-in function for demangling Swift symbol names, in the Runtime<\/code> module (that’s bundled with the Swift toolchain, alongside the stdlib etc).<\/p>\n<\/blockquote>\n\n

Khoa Pham<\/a>:<\/p>\n

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As Apple has aligned OS version numbers across platforms, Swift 6.4 takes the next step by letting you collapse repetitive availability attributes into a single anyAppleOS<\/code> token.<\/p>\n

[…]<\/p>\n

There are situations where you need to call a deprecated API while you plan a migration, or audit a critical function for unsafe usage, without letting those concerns bleed into the rest of the project. The new @diagnose<\/code> attribute handles both cases.<\/p>\n

[…]<\/p>\n

Some work should complete even after a task is cancelled, like flushing a file to avoid corruption. withTaskCancellationShield<\/code> wraps a region where Task.isCancelled<\/code> always returns false.<\/p>\n<\/blockquote>\n\n

Antoine van der Lee<\/a>:<\/p>\n

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Swift 6.4 implements SE-0493: Support async<\/code> calls in defer<\/code> bodies<\/a>. This is one of those changes that feels obvious once you need it.<\/p>\n

[…]<\/p>\n

Swift 6.4 improves error handling for unstructured tasks through SE-0520: Discardable result use in Task initializers<\/a>. The change helps you catch a subtle bug: creating a throwing task and then ignoring its returned task handle.<\/p>\n

[…]<\/p>\n

Swift 6.4 also implements SE-0530: Async Result Support<\/a>.<\/p>\n

[…]<\/p>\n

Swift 6.4 implements SE-0518: ~Sendable<\/code> for explicitly marking non-Sendable<\/code> types<\/a>. It allows you to communicate that a type has been audited and should not conform to Sendable<\/code>.<\/p>\n<\/blockquote>\n\n

Slava Pestov<\/a>:<\/p>\n

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I thought it would be a good time to detail some of the type checker performance improvements we worked on since I shared the type checker performance roadmap<\/a> last year. I’m also going to outline a couple of things we plan on looking at next.<\/p>\n<\/blockquote>\n\n

Previously:<\/p>\n