swift-actor-persistence

Topics in the source

• Swift Actors for Thread-Safe Persistence
• When to Activate
• Core Pattern
• Actor-Based Repository
• Usage
• Combining with @Observable ViewModel
• Key Design Decisions
• Best Practices

Patterns for building thread-safe data persistence layers using Swift actors. Combines in-memory caching with file-backed storage, leveraging the actor model to eliminate data races at compile time. Building a data persistence layer in Swift 5.5+ Need thread-safe access to shared mutable state Want to eliminate manual synchronization (locks, DispatchQueues) Building offline-first apps with local storage The actor model guarantees serialized access — no data races, enforced by the compiler. All calls are automatically async due to actor isolation: | Decision | Rationale | |----------|-----------| | Actor (not class + lock) | Compiler-enforced thread safety, no manual synchronization | | In-memory cache + file persistence | Fast reads from cache, durable writes to disk | | Synchronous init loading | Avoids async initialization complexity | | Dictionary keyed by ID | O(1) lookups by identifier | | Generic over Codable & Identifiable | Reusable across any model type | | Atomic file writes (.atomic) | Prevents partial writes on crash | Use Sendable types for all data crossing actor boundaries Keep the actor's public API minimal — only expose domain operations, not persistence details Us

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