how to create anotation like @MainActor

To create an annotation like @MainActor in Swift, you can use the @MainActor attribute to indicate that a particular piece of code should be executed on the main actor. This is particularly useful for UI-related code that must run on the main thread to avoid concurrency issues.

Here are some key points from the WWDC session "Migrate your app to Swift 6" that explain how to use @MainActor:

Annotating Methods and Properties: You can annotate methods or properties to indicate that they should be executed on the main actor. For example:
```
@MainActor
func updateUI() {
    // UI update code
}
```
Assume Isolated: If you know that a method will always be called on the main actor, you can use MainActor.assumeIsolated to inform the compiler:
```
MainActor.assumeIsolated {
    // Code that assumes it's running on the main actor
}
```
This does not start a new task but tells Swift that the code is already running on the main actor. This can help avoid unnecessary context switching.
Protocol Conformance: You can also annotate entire protocols to indicate that all conforming types should be isolated to the main actor:
```
@MainActor
protocol MyMainActorProtocol {
    func performTask()
}
```
Implicit Isolation: In Swift 6, many delegates and protocols, such as SwiftUI.View, are implicitly isolated to the main actor. This means you might not need to add @MainActor annotations explicitly if the protocol or delegate already guarantees main actor isolation.

For more detailed information, you can refer to the session Migrate your app to Swift 6 (19:29).

Relevant Sessions

These sessions provide comprehensive guidance on using @MainActor and other concurrency features in Swift 6.