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Updated SKILL.md to reference project concurrency settings and added a new reference guide for Swift 6.2 approachable concurrency mode. The new guide covers detection, expected behavior changes, recommended fixes, and common pitfalls for projects using main-actor-by-default and default actor isolation.
63 lines
2.4 KiB
Markdown
63 lines
2.4 KiB
Markdown
## Approachable Concurrency (Swift 6.2) - project mode quick guide
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Use this reference when the project has opted into the Swift 6.2 approachable
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concurrency settings (default actor isolation / main-actor-by-default).
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## Detect the mode
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Check Xcode build settings under "Swift Compiler - Concurrency":
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- Swift language version (must be 6.2+).
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- Default actor isolation / Main Actor by default.
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- Strict concurrency checking level (Complete/Targeted/Minimal).
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For SwiftPM, inspect Package.swift swiftSettings for the same flags.
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## Behavior changes to expect
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- Async functions stay on the caller's actor by default; they don't hop to a
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global concurrent executor unless the implementation chooses to.
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- Main-actor-by-default reduces data race errors for UI-bound code and global
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state, because mutable state is implicitly protected.
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- Protocol conformances can be isolated (e.g., `extension Foo: @MainActor Bar`).
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## How to apply fixes in this mode
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- Prefer minimal annotations; let main-actor-by-default do the work when the
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code is UI-bound.
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- Use isolated conformances instead of forcing `nonisolated` workarounds.
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- Keep global or shared mutable state on the main actor unless there is a clear
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performance need to offload it.
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## When to opt out or offload work
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- Use `@concurrent` on async functions that must run on the concurrent pool.
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- Make types or members `nonisolated` only when they are truly thread-safe and
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used off the main actor.
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- Continue to respect Sendable boundaries when values cross actors or tasks.
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## Common pitfalls
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- `Task.detached` ignores inherited actor context; avoid it unless you truly
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need to break isolation.
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- Main-actor-by-default can hide performance issues if CPU-heavy work stays on
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the main actor; move that work into `@concurrent` async functions.
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## Keywords (from source cheat sheet)
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| Keyword | What it does |
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| --- | --- |
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| `async` | Function can pause |
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| `await` | Pause here until done |
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| `Task { }` | Start async work, inherits context |
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| `Task.detached { }` | Start async work, no inherited context |
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| `@MainActor` | Runs on main thread |
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| `actor` | Type with isolated mutable state |
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| `nonisolated` | Opts out of actor isolation |
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| `Sendable` | Safe to pass between isolation domains |
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| `@concurrent` | Always run on background (Swift 6.2+) |
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| `async let` | Start parallel work |
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| `TaskGroup` | Dynamic parallel work |
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## Source
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https://fuckingapproachableswiftconcurrency.com/en/
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