SkillAtlasSkill 详情

swift-formatstyle

86 agent skills optimized for iOS 26+ development with Swift 6.

审核状态:已审核Quality 80Security 88

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项目 README

来源文件:README.md

抓取于 2026年8月22日

Swift iOS Skills — Agent Skills for iOS 26+ & SwiftUI Development

GitHub stars Swift 6.3 Platform Claude Code OpenAI Codex Agent Skills tessl License: PolyForm Perimeter

86 agent skills optimized for iOS 26+ development with Swift 6.3 and modern Apple frameworks. All code examples, patterns, and guidance target the latest APIs -- Liquid Glass, approachable concurrency, Foundation Models, StoreKit 2, SwiftData, async/await URLSession, and more. No deprecated patterns.

Compatible with Claude Code, OpenAI Codex, Cursor, GitHub Copilot, and 40+ other agents. Follows the open Agent Skills standard.

Every skill is self-contained. No skill depends on another. Install only what you need.

Release history: CHANGELOG.md.

Contents

Install

Recommended: any agent via skills CLI

The skills CLI is the recommended install method.

Interactive install (recommended):

npx skills add dpearson2699/swift-ios-skills

Running the default command opens the skills CLI UI so you can choose which skills to install and which agent(s) to install them for.

Install everything for any coding agent:

npx skills add dpearson2699/swift-ios-skills --all

Use --all when you want the full set of 86 skills installed automatically for any coding agent.

Install specific skills directly:

npx skills add dpearson2699/swift-ios-skills --skill <skill-name> --skill <skill-name>

Check for updates to installed skills:

npx skills check

Update installed skills to the latest versions:

npx skills update

Use these after installing through the skills CLI.

Claude Code (via plugin marketplace)

Add the marketplace (one-time):

/plugin marketplace add dpearson2699/swift-ios-skills

Install everything:

/plugin install all-ios-skills@swift-ios-skills

Or install a themed bundle (bundles limit how many skills load into the context window — if you want everything, use all-ios-skills above instead of installing multiple bundles):

/plugin install swiftui-skills@swift-ios-skills
/plugin install swift-core-skills@swift-ios-skills
/plugin install ios-app-framework-skills@swift-ios-skills
/plugin install ios-data-framework-skills@swift-ios-skills
/plugin install ios-ai-ml-skills@swift-ios-skills
/plugin install ios-engineering-skills@swift-ios-skills
/plugin install ios-hardware-skills@swift-ios-skills
/plugin install ios-platform-skills@swift-ios-skills
/plugin install ios-gaming-skills@swift-ios-skills
/plugin install apple-kit-skills@swift-ios-skills

OpenAI Codex

$skill-installer install https://github.com/dpearson2699/swift-ios-skills/tree/main/skills/<skill-name>

Claude Web App / Claude Desktop

  1. Download the skill folder(s) you want from this repo
  2. Zip each skill folder
  3. Go to Settings > Capabilities and enable "Code execution and file creation"
  4. Go to Customize > Skills, click +, then Upload a skill
  5. Upload the zip

ChatGPT

  1. Download the skill folder(s) you want from this repo
  2. Zip each skill folder
  3. Click your profile icon in ChatGPT and select Skills
  4. Click New skill and select Upload from your computer
  5. Upload the zip

Plugin Bundles (Claude Code)

PluginSkills included
all-ios-skillsAll 86 skills
apple-kit-skills39 skills spanning Apple Kit frameworks plus CarPlay
swiftui-skillsfocus-engine, swiftui-animation, swiftui-gestures, swiftui-layout-components, swiftui-liquid-glass, swiftui-navigation, swiftui-patterns, swiftui-performance, swiftui-uikit-interop, swiftui-webkit
swift-core-skillscore-data, swift-api-design-guidelines, swift-architecture, swift-codable, swift-charts, swift-concurrency, swift-formatstyle, swift-language, swift-testing, swiftdata
ios-app-framework-skillsactivitykit, adattributionkit, alarmkit, app-clips, app-intents, avkit, carplay, mapkit, paperkit, pdfkit, photokit, push-notifications, storekit, tipkit, widgetkit
ios-data-framework-skillscloudkit, contacts-framework, eventkit, financekit, healthkit, musickit, passkit, weatherkit
ios-ai-ml-skillsapple-on-device-ai, coreml, natural-language, speech-recognition, vision-framework
ios-engineering-skillsapp-store-optimization, app-store-review, authentication, background-processing, cryptokit, debugging-instruments, device-integrity, ios-accessibility, ios-ettrace-performance, ios-localization, ios-memgraph-analysis, ios-networking, swift-security, swiftlint, ios-simulator, metrickit
ios-hardware-skillsaccessorysetupkit, core-bluetooth, core-motion, core-nfc, dockkit, pencilkit, realitykit, sensorkit
ios-platform-skillsappmigrationkit, audioaccessorykit, browserenginekit, callkit, cryptotokenkit, energykit, homekit, permissionkit, relevancekit, shareplay-activities
ios-gaming-skillsgamekit, scenekit, spritekit, tabletopkit

Skills

SwiftUI

SkillWhat it covers
focus-engine@FocusState, defaultFocus, focusSection, focused scene values, focus restoration, UIFocusGuide
swiftui-animationSpring animations, PhaseAnimator, KeyframeAnimator, matchedGeometryEffect, SF Symbols
swiftui-gesturesTap, drag, magnify, rotate, long press, simultaneous and sequential gestures
swiftui-layout-componentsGrid, LazyVGrid, Layout protocol, ViewThatFits, custom layouts
swiftui-liquid-glassiOS 26 Liquid Glass, glassEffect, GlassEffectContainer, morphing transitions
swiftui-navigationNavigationStack, NavigationSplitView, programmatic navigation, deep linking
swiftui-patterns@Observable, state ownership, environment wiring, view composition, async loading, MV-pattern architecture
swiftui-performanceRendering performance, view update optimization, layout thrash, Instruments profiling
swiftui-uikit-interopUIViewRepresentable, UIHostingController, Coordinator, incremental UIKit-to-SwiftUI migration
swiftui-webkitWebView, WebPage, navigation policies, JavaScript calls, local content, custom URL schemes

Core Swift

SkillWhat it covers
swift-api-design-guidelinesSwift API Design Guidelines -- argument labels, mutating/nonmutating pairs, documentation comments, naming conventions
swift-architectureArchitecture patterns: MV (@Observable), MVVM, MVI, TCA, Clean Architecture, Coordinator, decision framework
swift-codableSwift Codable, JSONDecoder, JSONEncoder, CodingKeys, custom decoding, nested JSON
swift-chartsBar, line, area, pie, donut, and 3D charts, scrolling, selection, annotations
swift-concurrencySwift 6.2 concurrency, Sendable, actors, structured concurrency, data-race safety
swift-formatstyleFormatStyle protocol, number/currency/date/duration/measurement formatting, custom styles
swift-languageSwift 6.3 language idioms, result builders, property wrappers, typed throws
swift-testingSwift Testing framework, @Test, @Suite, #expect, parameterized tests, mocking
core-dataCore Data persistence, NSPersistentContainer, NSFetchedResultsController, batch operations, staged migration
swiftdata@Model, @Query, #Predicate, ModelContainer, migrations, CloudKit sync, @ModelActor

App Experience Frameworks

SkillWhat it covers
activitykitActivityKit, Dynamic Island, Lock Screen Live Activities, push-to-update
adattributionkitPrivacy-preserving ad attribution, postbacks, conversion values, re-engagement
alarmkitAlarmKit system alarms and countdown timers, Lock Screen, Dynamic Island, Live Activities
app-clipsApp Clips, invocation URLs, NFC, QR, App Clip Codes, App Group handoff
app-intentsApp Intents for Siri, Shortcuts, Spotlight, widgets, and Apple Intelligence
avkitAVPlayerViewController, VideoPlayer, Picture-in-Picture, AirPlay, subtitles
carplayCarPlay templates, navigation, audio, communication, EV charging apps
mapkitMapKit, CoreLocation, annotations, geocoding, directions, geofencing
paperkitPaperMarkupViewController, markup editing, drawing, shapes (iOS 26)
pdfkitPDFView, PDFDocument, annotations, text search, form filling, thumbnails
photokitPhotosPicker, AVCaptureSession, photo library, video recording, media permissions
push-notificationsUNUserNotificationCenter, APNs, rich notifications, silent push, service extensions
storekitStoreKit 2 purchases, subscriptions, SubscriptionStoreView, transaction verification
tipkitFeature discovery tooltips, contextual tips, tip rules, tip events
widgetkitHome Screen, Lock Screen, and StandBy widgets, Control Center controls, timeline providers

Data & Service Frameworks

SkillWhat it covers
cloudkitCKContainer, CKRecord, subscriptions, sharing, CKSyncEngine, SwiftData sync
contacts-frameworkCNContactStore, fetch requests, key descriptors, CNContactPickerViewController, save requests
eventkitEKEventStore, EKEvent, EKReminder, recurrence rules, EventKitUI editors and choosers
financekitApple Card, Apple Cash, Wallet orders, transaction queries, account balances
healthkitHKHealthStore, queries, statistics, workout sessions, background delivery
musickitMusicKit authorization, catalog search, ApplicationMusicPlayer, MPRemoteCommandCenter
passkitApple Pay, PKPaymentRequest, PKPaymentAuthorizationController, Wallet passes
weatherkitWeatherService, current/hourly/daily forecasts, alerts, attribution requirements

AI & Machine Learning

SkillWhat it covers
apple-on-device-aiFoundation Models framework, Core ML, MLX Swift, on-device LLM inference
coremlCore ML model loading, prediction, MLTensor, compute unit configuration, VNCoreMLRequest, MLComputePlan
natural-languageNLTokenizer, NLTagger, sentiment analysis, language identification, embeddings, Translation
speech-recognitionSpeechAnalyzer, SpeechTranscriber, SFSpeechRecognizer, on-device recognition, audio buffer processing
vision-frameworkVision text recognition, face/barcode detection, image segmentation, VisionKit DataScannerViewController

iOS Engineering

SkillWhat it covers
app-store-optimizationASO keyword strategy, description writing, screenshot optimization, Custom Product Pages, A/B testing
app-store-reviewApp Review guidelines, rejection prevention, privacy manifests, ATT, HIG compliance
authenticationSign in with Apple, ASAuthorizationController, passkeys, biometric auth (LAContext), credential management
background-processingBGTaskScheduler, background refresh, URLSession background transfers
cryptokitSHA-2/SHA-3, HMAC, AES-GCM, ChaChaPoly, HPKE, ML-KEM/ML-DSA, P256/Curve25519 signing, ECDH, Secure Enclave
debugging-instrumentsXcode debugger, Instruments, os_signpost, MetricKit, crash symbolication
device-integrityDeviceCheck (DCDevice per-device bits), App Attest (DCAppAttestService attestation and assertion flows)
ios-accessibilityVoiceOver, Dynamic Type, custom rotors, accessibility focus, assistive-technology support
ios-ettrace-performanceETTrace launch/runtime capture, exact-build dSYM matching, processed flamegraph JSON, comparable verification
ios-localizationString Catalogs, pluralization, FormatStyle, right-to-left layout
ios-memgraph-analysisSimulator memgraph capture, leak ownership paths, reachable heap growth, raw evidence preservation
ios-networkingURLSession async/await, REST APIs, downloads/uploads, WebSockets, pagination, retry, caching
swift-securityKeychain Services, CryptoKit symmetric/asymmetric, biometric authentication, Secure Enclave, certificate trust, credential storage, OWASP compliance · Based on ivan-magda/swift-security-skill
ios-simulatorxcrun simctl commands, device lifecycle, push/location/privacy simulation, log streaming, simulator limitations
metrickitMetricManager async reports, hang/crash diagnostics, production performance telemetry
swiftlintSwiftLint setup, .swiftlint.yml, build tool plugin, rule selection, baselines, suppressions, CI integration

Hardware & Device Integration

SkillWhat it covers
accessorysetupkitPrivacy-preserving BLE/Wi-Fi accessory discovery, ASAccessorySession, picker UI
core-bluetoothCBCentralManager, CBPeripheral, BLE scanning/connecting, services, characteristics, background modes
core-motionCMMotionManager, CMPedometer, accelerometer, gyroscope, activity recognition, altitude
core-nfcNFCNDEFReaderSession, NFCTagReaderSession, NDEF reading/writing, background tag reading
dockkitDockAccessoryManager, camera subject tracking, motor control, framing
pencilkitPKCanvasView, PKDrawing, PKToolPicker, Apple Pencil drawing and annotation
realitykitRealityView, entities, anchors, ARKit world tracking, raycasting, scene understanding
sensorkitResearch-grade sensor data, ambient light, keyboard metrics, device usage (approved studies)

Platform Integration

SkillWhat it covers
appmigrationkitCross-platform data transfer, AppMigrationExtension export/import (iOS 26)
audioaccessorykitAudio accessory features, automatic switching, device placement (iOS 26.4)
browserenginekitAlternative browser engines (EU), process management, web content extensions
callkitCXProvider, CXCallController, PushKit VoIP registration, call directory extensions
cryptotokenkitTKTokenDriver, TKSmartCard, iOS 26 NFC smart cards, certificate-based auth
energykitElectricityGuidance, EnergyVenue, grid forecasts, load event submission, electricity insights
homekitHMHomeManager, accessories, rooms, actions, triggers, MatterSupport commissioning
permissionkitAskCenter, PermissionQuestion, child communication safety, CommunicationLimits
relevancekitWidget relevance signals, time/location-based relevance providers (watchOS 26)
shareplay-activitiesGroupActivity, GroupSession, GroupSessionMessenger, coordinated media playback

Gaming

SkillWhat it covers
gamekitGame Center, GKLocalPlayer, leaderboards, achievements, real-time and turn-based multiplayer
scenekitSCNView, SCNScene, 3D geometry, materials, lighting, physics, SceneView
spritekitSKScene, SKSpriteNode, SKAction, physics simulation, particle effects, SpriteView
tabletopkitMultiplayer spatial board games, pieces, cards, dice, Group Activities (visionOS)

Structure

Each skill follows the open Agent Skills standard:

skills/
  skill-name/
    SKILL.md              # Required — instructions and metadata
    references/           # Optional — detailed reference material
      some-topic.md

SKILL.md contains YAML frontmatter (name, description) and markdown instructions. The references/ folder holds longer examples, advanced patterns, and lookup tables that the main file points to.

This repository contains original instructional content and examples for Apple platform development. Where Apple frameworks, APIs, documentation, WWDC sessions, or trademarks are referenced, those materials remain the property of Apple Inc. The license for this repository applies to this project's original content only and does not claim ownership of or relicense Apple's documentation, trademarks, sample code, or other third-party materials.

Compatibility

These skills work with any agent that supports the Agent Skills standard, including:

Upgrading from v2.x

v3.0 is a major release. If you previously installed v2.x skills, note the following changes:

  • Skill count: 57 skills in v2.2.0, 76 skills in v3.0.0.

  • Skill renames: 12 existing skills renamed to use Apple Kit framework names. Old skill paths no longer resolve. Uninstall all skills and reinstall to upgrade.

    v2.x namev3.0 name
    live-activitiesactivitykit
    mapkit-locationmapkit
    photos-camera-mediaphotokit
    homekit-matterhomekit
    callkit-voipcallkit
    metrickit-diagnosticsmetrickit
    pencilkit-drawingpencilkit
    passkit-walletpasskit
    musickit-audiomusickit
    cloudkit-synccloudkit
    eventkit-calendareventkit
    realitykit-arrealitykit
  • 19 new Kit framework skills: avkit, gamekit, cryptokit, pdfkit, paperkit, spritekit, scenekit, financekit, accessorysetupkit, adattributionkit, carplay, appmigrationkit, browserenginekit, dockkit, sensorkit, tabletopkit, relevancekit, audioaccessorykit, cryptotokenkit.

  • New bundles: apple-kit-skills (all 39 Apple Kit framework skills) and ios-gaming-skills (GameKit, SpriteKit, SceneKit, TabletopKit).

  • PaperKit standalone: PaperKit content removed from pencilkit and is now its own paperkit skill.

  • Beta frameworks: permissionkit, energykit, paperkit, relevancekit, appmigrationkit, and audioaccessorykit require iOS/watchOS 26 beta and are subject to API changes before GM.

  • All skills remain self-contained: No skill references or depends on another.

To upgrade via the skills CLI:

npx skills add dpearson2699/swift-ios-skills

To upgrade Claude Code bundles, reinstall the bundles you use (old skill paths will no longer resolve).

Support

If these skills save you time or improve your workflow, you can support ongoing maintenance through GitHub Sponsors.

Support helps keep the collection current with new Apple releases, evolving framework APIs, updated examples, and compatibility work across Claude Code, Codex, Cursor, Copilot, and other agents.

Sponsors

Thanks to the following people for supporting this project:

Anthony Jr.

License

PolyForm Perimeter 1.0.0 -- see LICENSE

What this means in practice:

  • Using these skills to build your iOS app -- allowed
  • Using these skills inside a closed-source commercial workflow -- allowed
  • Forking the repo and contributing back -- allowed
  • Sharing the skills with a teammate -- allowed
  • Taking the skills, rebranding them as "Premium iOS Agent Skills," and selling them -- not allowed (that's a competing product)

This project is not affiliated with, endorsed by, or sponsored by Apple Inc.

测试与质量

中风险

  • 来源需自行核对维护者身份。
  • 未检测到明显脚本安装指令。
  • 未检测到明显外部权限要求。
  • 未检测到高风险命令。
  • 扫描发现:1 条。

Codex — Git Clone 安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 克隆仓库:git clone https://github.com/dpearson2699/swift-ios-skills.git
  3. 将 "skills/swift-formatstyle" 文件夹复制到 Codex 的 skills 目录中。
  4. 重启 Codex 让新的 skill 生效。

Codex — 手动复制安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 从源仓库下载 SKILL.md 及相关文件。
  3. 在 Codex 的 skills 目录中创建新文件夹。
  4. 将所有 skill 文件复制到新文件夹中。
  5. 重启 Codex 让新的 skill 生效。

Claude Code — Git Clone 安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 克隆仓库:git clone https://github.com/dpearson2699/swift-ios-skills.git
  3. 将 "skills/swift-formatstyle" 文件夹复制到 Claude Code 的 skills 目录中。
  4. 重启 Claude Code 让新的 skill 生效。

Claude Code — 手动复制安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 从源仓库下载 SKILL.md 及相关文件。
  3. 在 Claude Code 的 skills 目录中创建新文件夹。
  4. 将所有 skill 文件复制到新文件夹中。
  5. 重启 Claude Code 让新的 skill 生效。

Cursor — Git Clone 安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 克隆仓库:git clone https://github.com/dpearson2699/swift-ios-skills.git
  3. 将 "skills/swift-formatstyle" 文件夹复制到 Cursor 的 skills 目录中。
  4. 重启 Cursor 让新的 skill 生效。

Cursor — 手动复制安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 从源仓库下载 SKILL.md 及相关文件。
  3. 在 Cursor 的 skills 目录中创建新文件夹。
  4. 将所有 skill 文件复制到新文件夹中。
  5. 重启 Cursor 让新的 skill 生效。

GitHub Copilot — Git Clone 安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 克隆仓库:git clone https://github.com/dpearson2699/swift-ios-skills.git
  3. 将 "skills/swift-formatstyle" 文件夹复制到 GitHub Copilot 的 skills 目录中。
  4. 重启 GitHub Copilot 让新的 skill 生效。

GitHub Copilot — 手动复制安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 从源仓库下载 SKILL.md 及相关文件。
  3. 在 GitHub Copilot 的 skills 目录中创建新文件夹。
  4. 将所有 skill 文件复制到新文件夹中。
  5. 重启 GitHub Copilot 让新的 skill 生效。

Windsurf — Git Clone 安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 克隆仓库:git clone https://github.com/dpearson2699/swift-ios-skills.git
  3. 将 "skills/swift-formatstyle" 文件夹复制到 Windsurf 的 skills 目录中。
  4. 重启 Windsurf 让新的 skill 生效。

Windsurf — 手动复制安装

  1. 安装前请先查看来源仓库和风险报告。
  2. 从源仓库下载 SKILL.md 及相关文件。
  3. 在 Windsurf 的 skills 目录中创建新文件夹。
  4. 将所有 skill 文件复制到新文件夹中。
  5. 重启 Windsurf 让新的 skill 生效。
查看 SKILL.md 原文
name: swift-formatstyle
description: "Formats and parses locale-aware numbers, decimals, currencies, percentages, dates, durations, measurements, names, lists, byte counts, and URLs with Foundation FormatStyle and ParseableFormatStyle. Use when replacing legacy Formatter subclasses, designing reusable format APIs, using SwiftUI Text(_:format:), correcting availability, or testing user-facing formatted output across locales."

Swift FormatStyle

Use Foundation's type-safe FormatStyle APIs for user-facing display and ParseableFormatStyle when the same convention must accept input. Route String Catalogs, plurals, localized copy, bundles, and RTL layout to ios-localization; formatting still requires locale review even when no text is translated.

Contents

Workflow

  1. Identify the value's semantic type and whether output is display-only or must round-trip through parsing.
  2. Select the narrowest built-in style and keep the user's current locale unless a wire format explicitly requires another locale.
  3. Render the exact UI with representative locales such as en_US, de_DE, ar_SA, and ja_JP.
  4. Check separators, numbering systems, calendars, currency and unit conventions, text direction, and layout.
  5. If output or parsing fails, fix the style or surrounding copy, restore the input fixture, and rerun the same locale matrix.

Load FormatStyle Recipes when implementation needs concrete modifiers, date intervals, relative dates, duration patterns, measurements, names, lists, byte counts, or URL component controls.

Quick Reference

ValueDefault styleImportant constraint
Int, Double.numberConfigure precision, rounding, grouping, notation, or sign only as required.
Decimal.number, .percent, .currency(code:)Prefer for exact decimal display and parsing.
Currency.currency(code:)Pass an ISO 4217 code; never hardcode a symbol.
Percent.percentConfirm whether the input is a fraction (0.85) or whole percent (85).
Date.dateTime, .relative, .intervalRelative output should usually stand alone, not be embedded in a sentence.
Duration.time(pattern:), .units(allowed:width:)Requires iOS 16+; choose compact clock output versus labeled units.
Measurement.measurement(width:usage:)usage: controls locale-aware conversion policy.
PersonNameComponents.name(style:)Do not manually concatenate name parts.
Collections.list(type:width:)Let locale rules choose separators and conjunctions.
Byte count.byteCount(style:)Choose file, memory, decimal, or binary semantics deliberately.
URL.urlRequires iOS 16+; query, port, and fragment are opt-in display components.

Selection and Availability

  • Prefer FormatStyle over legacy NumberFormatter, DateFormatter, DateComponentsFormatter, and manual interpolation for new iOS 15+ code.
  • Duration format styles and URL.FormatStyle require iOS 16+.
  • Date.AnchoredRelativeFormatStyle requires iOS 18+ and formats relative to a fixed anchor rather than the current moment.
  • Omit .locale(...) for normal UI so the style inherits the user's locale. Use a fixed locale only for an explicit protocol or test fixture.
  • Treat relative date output as standalone text unless the entire sentence is localized around it.

Docs: FormatStyle

Parsing

Use the matching parseable style when users edit or import formatted values:

let style = Decimal.FormatStyle.Currency(code: "USD")
    .locale(Locale(identifier: "en_US"))

let value = try Decimal("$3,500.63", format: style)
let display = value.formatted(style)

The fixed locale above is appropriate only because the input contract is explicitly en_US. For normal UI input, use the user's locale and test round trips with representative decimal separators, currency placement, calendars, and numbering systems.

SwiftUI Integration

Prefer Text(_:format:) so SwiftUI owns the formatted value:

Text(price, format: .currency(code: currencyCode))
Text(date, format: .dateTime.month().day().year())
Text(duration, format: .units(allowed: [.minutes, .seconds]))

For every user-facing formatted Text, preview or test the exact screen across the locale matrix. Use Text(.now, style: .timer), Text(.now, style: .relative), or Text(timerInterval:) for live-updating time displays rather than manually scheduling string refreshes.

Custom FormatStyle

Create a custom style only when built-in composition cannot express the domain convention. FormatStyle refines Codable and Hashable; keep styles as reusable values and add ParseableFormatStyle only when input must round-trip.

struct AbbreviatedCountStyle: FormatStyle {
    func format(_ value: Int) -> String {
        switch value {
        case ..<1_000: "\(value)"
        case 1_000..<1_000_000: String(format: "%.1fK", Double(value) / 1_000)
        default: String(format: "%.1fM", Double(value) / 1_000_000)
        }
    }
}

extension FormatStyle where Self == AbbreviatedCountStyle {
    static var abbreviatedCount: Self { .init() }
}

Custom styles still need locale and accessibility review; a compact English suffix may not be suitable for every locale.

Common Mistakes

MistakeFix
Manual formatting or legacy formatter allocation in view codeUse the matching FormatStyle and Text(_:format:).
Hardcoded currency symbol or localePass an ISO currency code and inherit the user locale unless the contract says otherwise.
Binary floating-point for exact decimal inputUse Decimal.FormatStyle and its matching parse strategy.
Assuming URL.formatted() preserves every componentOpt in to .port(.always), .query(.always), or .fragment(.always) only when those components should display.
Relative date output embedded in a larger sentenceKeep it standalone or localize the complete sentence.
Clock-style duration used for proseUse .units(allowed:width:) for labeled output.
Measurement conversion left implicitSelect a usage: appropriate to the UI.
One-locale spot checkRun the same exact-screen fixture across representative locales and fix/rerun failures.

Review Checklist

  • Semantic value type and display-versus-parse requirement identified
  • Built-in FormatStyle used where it can express the convention
  • Availability gated beside iOS 16+ and iOS 18+ APIs
  • Currency uses an ISO 4217 code; exact decimal values use Decimal
  • User locale inherited unless a protocol explicitly fixes it
  • Relative date text stands alone or the full sentence is localized
  • URL components and measurement usage: are deliberate
  • SwiftUI uses Text(_:format:) for formatted values
  • Exact rendered UI and parse round trips pass the representative-locale matrix

References

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