Swift Actor Persistence

This is a practical pattern for local data persistence in Swift 5.5+ that uses actors instead of manual locks or DispatchQueues. You get an in-memory dictionary cache backed by JSON file storage, with compile-time guarantees against data races. The generic repository works with any Codable and Identifiable type, giving you O(1) lookups and atomic file writes. It's most useful for offline-first apps or anywhere you need thread-safe access to shared state without the ceremony of traditional synchronization primitives. The synchronous init load is a reasonable tradeoff that avoids async initialization complexity for local files.

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last updated: Jul 14, 2026

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Install

$ npx -y skills add affaan-m/everything-claude-code --skill swift-actor-persistence --agent claude-code

Installs into .claude/skills of the current project.

Files

Swift Actors for Thread-Safe Persistence

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.

When to Activate

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

Core Pattern

Actor-Based Repository

The actor model guarantees serialized access — no data races, enforced by the compiler.

public actor LocalRepository<T: Codable & Identifiable> where T.ID == String {
    private var cache: [String: T] = [:]
    private let fileURL: URL

    public init(directory: URL = .documentsDirectory, filename: String = "data.json") {
        self.fileURL = directory.appendingPathComponent(filename)
        // Synchronous load during init (actor isolation not yet active)
        self.cache = Self.loadSynchronously(from: fileURL)
    }

    // MARK: - Public API

SKILL.md on GitHub