Sharing

Point-Free's swift-sharing gives one value a single storage location and many observers. It is the layer SQLiteData's @FetchAll and @FetchOne are built on, and it works on its own for user defaults, files, and in-memory state.

When to Use

Use this skill when:

• A value is read in several places and must stay in sync — user settings, feature flags, the signed-in user
• You want to persist to UserDefaults or a file without hand-writing the load, save, and observe loop
• You need to know why @FetchAll is empty — still loading, or failed
• You are writing a custom persistence strategy, such as Keychain-backed or remote-config-backed storage
• A build broke after upgrading Xcode with an error about a @Shared setter

Example Prompts

• "How do I persist a setting to UserDefaults and observe it from several views?"
• "My @FetchAll is empty. Is it still loading, or did the query fail?"
• "After upgrading Xcode, Toggle(isOn: $settings.isEnabled) no longer compiles. What changed?"
• "How do I store an auth token with @Shared but keep it in the Keychain?"
• "How do I stop my tests from writing to the real UserDefaults?"

What This Skill Provides

• @Shared versus @SharedReader, and how to derive narrower references from either
• Using @Shared inside an @Observable class, where @ObservationIgnored is required
• The three built-in strategies — .appStorage, .fileStorage, .inMemory — and their traps, including the key-format rule that degrades cross-process observation (with a runtime warning) and the single-suite-instance rule
• Type-safe keys that register a default, so call sites carry no key strings
• Mutation through withLock and Binding($shared), and the Swift 6.3 change that turned the old setter path into a compile error below Sharing 2.8.0
• Loading and error state: isLoading, loadError, saveError, and why every non-optional @Shared needs a default
• Dynamic keys — swapping the backing key at runtime to re-drive a search
• Writing a custom SharedKey or SharedReaderKey, including continuation rules
• Per-test storage quarantine and the UI-test entry-point setup
• Package traits (CustomDump, IdentifiedCollections, CasePaths) and the Swift 6.1 manifest requirement

Documentation Scope

This page documents the swift-sharing skill (in the axiom-data suite) — the patterns your assistant draws on when a value has to persist and stay in sync across your app.

Related

• sqlitedata – @FetchAll and @FetchOne wrap a Sharing SharedReader, so the loading and error APIs documented here apply to every SQLiteData fetch
• sqlitedata-ref – advanced query composition on top of those property wrappers
• keychain – where secrets belong; reach them from @Shared through a custom key, never .appStorage

Resources

GitHub: pointfreeco/swift-sharing, pointfreeco/sqlite-data