Task.startOnMainActor.swift

public extension Task where Failure == Never {

    /// Create and immediately start running a new detached task on the @MainActor.
    ///
    /// If the current actor is @MainActor, the spawned task immediately takes over
    /// execution in a synchronous manner, before returning to the calling method at the
    /// first suspension point.
    ///
    /// If the current actor is not @MainActor then behaviour is the similar to using `Task { }`
    ///
    @available(iOS, deprecated: 26.0, message: "use Task.immediate")
    @MainActor
    @discardableResult
    static func immediateMainActor(
        priority: TaskPriority? = nil,
        operation: sending @escaping @MainActor () async -> Success
    ) -> Task<Success, Never> {
        if #available(iOS 26, *) {
            Task.immediate(priority: priority, operation: operation)
        } else {
            Task.startOnMainActor(priority: priority) { await operation() }
        }
    }
}

public extension Task where Failure == any Error {

    /// Create and immediately start running a new detached task on the @MainActor.
    ///
    /// If the current actor is @MainActor, the spawned task immediately takes over
    /// execution in a synchronous manner, before returning to the calling method at the
    /// first suspension point.
    ///
    /// If the current actor is not @MainActor then behaviour is the similar to using `Task { }`
    ///
    @available(iOS, deprecated: 26.0, message: "use Task.immediate")
    @MainActor
    @discardableResult
    static func immediateMainActor(
        priority: TaskPriority? = nil,
        operation: sending @escaping @MainActor () async throws -> Success
    ) -> Task<Success, any Error> {
        if #available(iOS 26, *) {
            Task.immediate(priority: priority, operation: operation)
        } else {
            Task.startOnMainActor(priority: priority) { try await operation() }
        }
    }
}

// Task.startOnMainActor shipped in iOS 17/18 as private api behind @_spi(MainActorUtilities).
// While the SDK swiftinterface strips this method, we can use the mangled name to link
// to the symbol at compile time
extension Task where Failure == Never {
    @_silgen_name("$sScTss5NeverORs_rlE16startOnMainActor8priority_ScTyxABGScPSg_xyYaYbScMYccntFZ")
    @MainActor
    @discardableResult
    public static func startOnMainActor(
        priority: TaskPriority? = nil,
        @_inheritActorContext @_implicitSelfCapture _ work: consuming @Sendable @escaping @MainActor() async -> Success
    ) -> Task<Success, Never>
}

extension Task where Failure == any Error {
	@_silgen_name("$sScTss5Error_pRs_rlE16startOnMainActor8priority_ScTyxsAA_pGScPSg_xyYaYbKScMYccntFZ")
    @MainActor
    @discardableResult
    public static func startOnMainActor(
        priority: TaskPriority? = nil,
        @_inheritActorContext @_implicitSelfCapture _ work: consuming @Sendable @escaping @MainActor() async throws -> Success
    ) -> Task<Success, any Error>
}