What is @Sendable in Swift?

@Sendable marks closures/functions safe for concurrency: captures must be Sendable types, by value via lists—no mutable refs across isolation domains.

How do I fix 'Reference to captured var in concurrently-executing code'?

Add capture list [x] for snapshot copy, ensure x is Sendable. Or refactor to immutable let.

Do all closures need @Sendable?

Only those crossing domains: actor args, Task captures, async handoffs. Single-threaded

💻 Programming Languages

Swift's @Sendable: The Passport Closures Need for Concurrency Chaos

Swift promised concurrency nirvana with actors and async/await. But closures? They were smuggling unsafe state across domains. @Sendable slams the door on bugs.

theAIcatchup Apr 10, 2026 4 min read

Swift closure with @Sendable crossing actor isolation boundaries

⚡ Key Takeaways

@Sendable ensures closures capture only safe, copyable values—no mutable heap boxes across concurrency domains. 𝕏
Use capture lists like [x] for vars to create immutable snapshots, dodging compiler errors. 𝕏
Powers real actor patterns: filters, maps, transforms in background Tasks without races. 𝕏

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#@Sendable #Swift #Swift actors #Swift concurrency #actor isolation #actors #closures #closures capture #concurrency #data races

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Originally reported by Dev.to

⚡ Key Takeaways

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