protect mutable state

To protect mutable state in Swift, especially in the context of concurrency, several strategies are discussed in the WWDC sessions:

1. Main Actor: Annotating an entire class with the main actor can protect all of its mutable state. This is particularly useful in projects that don't have a lot of concurrent tasks. The main actor ensures that global and static variables are safe from data races by default. This approach is recommended for apps, scripts, and other executable targets where most work is done on the main actor, and concurrent code is encapsulated within specific types or files. This feature is opt-in and helps reduce concurrency annotations in mostly single-threaded code. (What’s new in Swift)

2. Sendable Value Types: When sharing mutable state between concurrent code, using sendable value types can prevent data races. Sendable types ensure that the state is protected from concurrent accesses. If a type is not sendable, you might need to manually add synchronization or use actors to encapsulate shared mutable state. (A Swift Tour: Explore Swift’s features and design)

3. Swift 6 Language Mode: This mode introduces full enforcement of data isolation, preventing accidental sharing of state between tasks and actors. It helps catch concurrency bugs at compile time, improving the quality of your app. (Migrate your app to Swift 6)

4. Isolated Conformances: These are used when a conformance needs main actor state, ensuring that it is only used on the main actor. This helps solve data race safety issues when the code indicates concurrent use. (What’s new in Swift)

5. Concurrency Features in Swift 6: Swift 6 provides tools to prevent data races, such as isolating state to actors and using structured concurrency to control asynchronous code. (Code-along: Elevate an app with Swift concurrency)

These strategies collectively help in managing and protecting mutable state in Swift applications, especially when dealing with concurrency.