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Agent skill

Swift Actor Persistence

by affaan-m in affaan-m/ECC

Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design.

MITAuto-check passedMobile

Install Swift Actor Persistence

skills CLI
$ npx skills add affaan-m/ECC --skill swift-actor-persistence -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install affaan-m/ECC swift-actor-persistence --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/affaan-m/ECC.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/swift-actor-persistence .claude/skills/swift-actor-persistence && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
swift-actor-persistence
GitHub stars
277k
Used in
4 other repos
Token cost
~1.2k tokens
SKILL.md length
307 words
Files
1
Skills in repo
683
Repo updated
First seen
Licence
MIT

At a glance

Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design.

  • Persisting data in Swift and a data race
  • SKILL.md covers When to Activate, Core Pattern, Key Design Decisions and Best Practices, plus 2 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Thread-safety problem needs designing out

What it does

Swift Actor Persistence is an agent skill from affaan-m/ECC. Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design. Use when persisting data in Swift and a data race or thread-safety problem needs designing out.

Its SKILL.md is about 1.2k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Mobile, covering iOS development. The repository describes itself as: The agent harness performance optimization system. Skills, instincts, memory, security, and research-first development for Claude Code, Codex, Opencode, Cursor and beyond. The licence is MIT.

When your agent uses it

  • Persisting data in Swift and a data race
  • Thread-safety problem needs designing out

Example prompts

  • “/swift-actor-persistence”

What it can do on your machine

Read from SKILL.md and the folder at commit 2d515e4. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are swift).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Swift Actor Persistence loads about 1.2k tokens when it runs. Until then it costs about 62 tokens; SKILL.md has 307 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~62
When it runs · the whole SKILL.md, loaded when a task matches
~1.2k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from affaan-m/ECC at commit 2d515e4, republished under its MIT licence (© affaan-m). 307 words, ~1,223 tokens.

Download SKILL.mdSave it as .claude/skills/swift-actor-persistence/SKILL.md (or your agent's skills folder).
name
swift-actor-persistence
description
Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design. Use when persisting data in Swift and a data race or thread-safety problem needs designing out.
metadata.origin
ECC

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.

swift
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

    public func save(_ item: T) throws {
        cache[item.id] = item
        try persistToFile()
    }

    public func delete(_ id: String) throws {
        cache[id] = nil
        try persistToFile()
    }

    public func find(by id: String) -> T? {
        cache[id]
    }

    public func loadAll() -> [T] {
        Array(cache.values)
    }

    // MARK: - Private

    private func persistToFile() throws {
        let data = try JSONEncoder().encode(Array(cache.values))
        try data.write(to: fileURL, options: .atomic)
    }

    private static func loadSynchronously(from url: URL) -> [String: T] {
        guard let data = try? Data(contentsOf: url),
              let items = try? JSONDecoder().decode([T].self, from: data) else {
            return [:]
        }
        return Dictionary(uniqueKeysWithValues: items.map { ($0.id, $0) })
    }
}
Usage

All calls are automatically async due to actor isolation:

swift
let repository = LocalRepository<Question>()

// Read — fast O(1) lookup from in-memory cache
let question = await repository.find(by: "q-001")
let allQuestions = await repository.loadAll()

// Write — updates cache and persists to file atomically
try await repository.save(newQuestion)
try await repository.delete("q-001")
Combining with @Observable ViewModel
swift
@Observable
final class QuestionListViewModel {
    private(set) var questions: [Question] = []
    private let repository: LocalRepository<Question>

    init(repository: LocalRepository<Question> = LocalRepository()) {
        self.repository = repository
    }

    func load() async {
        questions = await repository.loadAll()
    }

    func add(_ question: Question) async throws {
        try await repository.save(question)
        questions = await repository.loadAll()
    }
}

Key Design Decisions

DecisionRationale
Actor (not class + lock)Compiler-enforced thread safety, no manual synchronization
In-memory cache + file persistenceFast reads from cache, durable writes to disk
Synchronous init loadingAvoids async initialization complexity
Dictionary keyed by IDO(1) lookups by identifier
Generic over Codable & IdentifiableReusable across any model type
Atomic file writes (.atomic)Prevents partial writes on crash

Best Practices

  • Use Sendable types for all data crossing actor boundaries
  • Keep the actor's public API minimal — only expose domain operations, not persistence details
  • Use .atomic writes to prevent data corruption if the app crashes mid-write
  • Load synchronously in init — async initializers add complexity with minimal benefit for local files
  • Combine with @Observable ViewModels for reactive UI updates

Anti-Patterns to Avoid

  • Using DispatchQueue or NSLock instead of actors for new Swift concurrency code
  • Exposing the internal cache dictionary to external callers
  • Making the file URL configurable without validation
  • Forgetting that all actor method calls are await — callers must handle async context
  • Using nonisolated to bypass actor isolation (defeats the purpose)

When to Use

  • Local data storage in iOS/macOS apps (user data, settings, cached content)
  • Offline-first architectures that sync to a server later
  • Any shared mutable state that multiple parts of the app access concurrently
  • Replacing legacy DispatchQueue-based thread safety with modern Swift concurrency

© affaan-m, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/swift-actor-persistence of affaan-m/ECC.

Open the folder on GitHubat commit 2d515e4

Used in 4 other repositories

We found 11 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 4 other GitHub owners. This page covers the copy in affaan-m/ECC, which our catalogue first saw on October 7, 2026.

Compare with similar skills

Swift Actor Persistence next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Swift Actor Persistence compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Swift Actor Persistence this skillaffaan-m/ECC277k4 repos~1.2kAutomated safety check: PassMIT
Swiftui Protwostraws/SwiftUI-Agent-Skill5.6k2 repos~1.5kAutomated safety check: PassMIT
Swiftui UI PatternsAFK-surf/OpenBridge4304 repos~887Automated safety check: PassMIT
Swiftui Performance Auditharperreed/dotfiles3348 repos~1.4kAutomated safety check: PassNone
Swift Testing ExpertAvdLee/Swift-Testing-Agent-Skill4711 repos~1.2kAutomated safety check: PassMIT
Hig Project Contextraintree-technology/hig-doctor1445 repos~1.2kAutomated safety check: PassMIT

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Categories

Questions about Swift Actor Persistence

What does Swift Actor Persistence do?

Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design. Swift Actor Persistence is an agent skill from affaan-m/ECC. Thread-safe data persistence in Swift using actors — in-memory cache with file-backed storage, eliminating data races by design.

When should I use Swift Actor Persistence?

Swift Actor Persistence fits situations like: persisting data in Swift and a data race; thread-safety problem needs designing out.

How do I install Swift Actor Persistence in Claude Code?

Run `npx skills add affaan-m/ECC --skill swift-actor-persistence -a claude-code`. Or copy the skill folder (skills/swift-actor-persistence in affaan-m/ECC) into .claude/skills/swift-actor-persistence in your project. Claude Code loads it when a task matches its description.

How do I install Swift Actor Persistence in Codex?

Run `npx skills add affaan-m/ECC --skill swift-actor-persistence -a codex`. Or copy the skill folder (skills/swift-actor-persistence in affaan-m/ECC) into .agents/skills/swift-actor-persistence in your project. Codex loads it when a task matches its description.

Can I use Swift Actor Persistence in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add affaan-m/ECC --skill swift-actor-persistence -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/swift-actor-persistence, .gemini/skills/swift-actor-persistence, .github/skills/swift-actor-persistence and .opencode/skills/swift-actor-persistence in your project.

What does Swift Actor Persistence need to run?

SKILL.md names no scripts, command-line tools or credentials: Swift Actor Persistence is instructions for the agent only.

Does Swift Actor Persistence access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Swift Actor Persistence safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Swift Actor Persistence use?

Swift Actor Persistence is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Swift Actor Persistence use?

About 1.2k tokens (SKILL.md is roughly 4.9k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Swift Actor Persistence?

Skills that share tags, products or a category with Swift Actor Persistence: Swiftui Pro (twostraws/SwiftUI-Agent-Skill, 5.6k stars), Swiftui UI Patterns (AFK-surf/OpenBridge, 430 stars), Swiftui Performance Audit (harperreed/dotfiles, 334 stars) and Swift Testing Expert (AvdLee/Swift-Testing-Agent-Skill, 471 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Swift Actor Persistence?

affaan-m (a GitHub user) maintains it in affaan-m/ECC, which has 276,673 GitHub stars. The repository holds 683 skills in this directory. The repository was last updated on October 11, 2026.

Source: affaan-m/ECC on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.