Task vs Task.detached

Apr 13, 2026 |

swift concurrency async ios

Both create unstructured tasks. Three things differ.

Actor isolation

Task inherits the actor context of its creator. Task.detached is always nonisolated.

actor Counter {
    var value = 0

    func increment() {
        Task { value += 1 }          // runs on Counter actor ✓
        Task.detached { value += 1 } // compile error — crosses actor boundary ✗
    }
}

Task locals

Task inherits task-local values from the calling context. Task.detached starts with no task locals.

@TaskLocal static var requestID: String = ""

TaskLocal.$requestID.withValue("abc") {
    Task { print(requestID) }          // "abc"
    Task.detached { print(requestID) } // ""
}

Priority

Task inherits the priority of its creator. Task.detached defaults to .medium unless specified explicitly.

Task { }                                    // inherits caller priority
Task.detached { }                           // .medium
Task.detached(priority: .background) { }    // explicit

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When you want fire-and-forget work that’s aware of its context — use Task. When you explicitly want isolation from the current actor and environment — use Task.detached.

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