what is actor isolation?

Actor isolation in Swift is a concurrency model that ensures that only one task can access an actor's state at a time, thereby preventing data races and ensuring thread safety. Actors are similar to classes in that they are reference types that can encapsulate shared mutable state. However, actors automatically protect their state by serializing accesses, meaning that only a single task is allowed to execute at a time on an actor. Calls to actor methods from outside the context of the actor are asynchronous.

For example, in the session A Swift Tour: Explore Swift’s features and design, it is explained that actors serialize accesses to their state, ensuring that only one task can execute at a time on an actor. This makes concurrent accesses to shared state safe.

In the session Migrate your app to Swift 6, it is highlighted that Swift 6 introduces full enforcement of data isolation, preventing accidental sharing of state between tasks and actors. This helps in catching concurrency bugs at compile time, improving the quality of the app.

Additionally, the concept of "assume isolated" is discussed in the same session, which allows developers to tell the compiler that a certain piece of code is already running on a specific actor, without starting a new task. This is useful for ensuring that certain methods are always called on the main actor, for example.

For more detailed information, you can refer to the chapter on Concurrency in the session "A Swift Tour: Explore Swift’s features and design" and the chapter on Delegate callbacks and concurrency in the session "Migrate your app to Swift 6".