gistfile1.txt

extension MainActor {
  public static func assumeIsolated<T : Sendable>(
      _ operation: @MainActor () throws -> T,
      file: StaticString = #fileID, line: UInt = #line
  ) rethrows -> T {
    typealias YesActor = @MainActor () throws -> T
    typealias NoActor = () throws -> T

    let executor: Builtin.Executor = unsafe Self.shared.unownedExecutor.executor
    guard _taskIsCurrentExecutor(executor) else {
      #if !$Embedded
      fatalError("Incorrect actor executor assumption; Expected same executor as \(self).", file: file, line: line)
      #else
      Builtin.int_trap()
      #endif
    }

    // To do the unsafe cast, we have to pretend it's @escaping.
    return try withoutActuallyEscaping(operation) {
      (_ fn: @escaping YesActor) throws -> T in
      let rawFn = unsafe unsafeBitCast(fn, to: NoActor.self)
      return try rawFn()
    }
  }
}