Async/Await: is it possible to start a Task on @MainActor synchronously?

Using Swift
9

Maybe MainActor will change its behavior, and start running synchronously when it can, yes.

But if I understand @ktoso well, at the time custom executors become public, we'd become able to write, outside of the stdlib, in our own application or library code, a custom global actor that does what we need:

@MainActor // (sic)
func someSynchronousUIKitOrSwiftUICallback() {
  Task { @UIActor in // (sic) a custom global actor
    for await value in someAsyncSequence {
      // handle value
    }
  }
  // <- Here values that were produced synchronously
  // are already handled, and UIKit/SwiftUI has been
  // correctly instructed.
}

This custom UIActor would play exactly the same role as those existing tools:

They exist for a well identified reason: they help developers program asynchronously within the constraints of frameworks like UIKit or SwiftUI.

In UIKit or SwiftUI, a missed opportunity from one of their synchronous callbacks usually means a degraded experience for the app user or the developer, from a blank frame on screen, to a need to explicitly code against double-taps.

Combine and RxSwift exist independently of UIKit or SwiftUI, and yet they provide the sharp and necessary tools for a seamless integration. I'm very eager to see Swift concurrency fill the gap with custom executors.

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