Swift Concurrency Expert

Attribution: copied from @Dimillian’s Dimillian/Skills (2025-12-31).

Overview

Review and fix Swift Concurrency issues in Swift 6.2+ codebases by applying actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes.

Workflow

1. Triage the issue

Capture the exact compiler diagnostics and the offending symbol(s).
Identify the current actor context (@MainActor, actor, nonisolated) and whether a default actor isolation mode is enabled.
Confirm whether the code is UI-bound or intended to run off the main actor.

2. Apply the smallest safe fix

Prefer edits that preserve existing behavior while satisfying data-race safety.

Common fixes:

UI-bound types: annotate the type or relevant members with @MainActor.
Protocol conformance on main actor types: make the conformance isolated (e.g., extension Foo: @MainActor SomeProtocol).
Global/static state: protect with @MainActor or move into an actor.
Background work: move expensive work into a @concurrent async function on a nonisolated type or use an actor to guard mutable state.
Sendable errors: prefer immutable/value types; add Sendable conformance only when correct; avoid @unchecked Sendable unless you can prove thread safety.

Reference material