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SkillPatterns — the compile-checked reference

Every Swift snippet in docs/ is prose. This package is the subset that actually builds, so CI can prove the patterns compile rather than asserting they do.

That distinction is the point. See docs/orchestration/verification.md.

cd samples/SkillPatterns
swift build
swift test

What it proves

Rule Where
@MainActor @Observable final class view models ArticleListModel.swift
Dependencies as any Protocol, injected, no live defaults ArticleListModel.swift, Composition.swift
Presentation never names a concrete repository or client ArticleListModel.swift
Inbound and outbound boundary protocols Domain.swift
Composition root as a protocol, not a singleton Composition.swift
CancellationError as a deliberate no-op ArticleListModel.swift
No catch { }, no error = nil throughout
Re-solve identity after an await (no stale indices) ArticleListModel.toggleBookmark
Single in-flight task, superseded not raced ArticleListModel.load
Typed Hashable, Codable routes Router.swift
Deep-link parsing as a pure, testable function Router.swift
Actor test doubles reconfigurable after injection Composition.swift
Fixtures with stable identity — a computed var re-randomises id Composition.swift
@Model kept distinct from the Sendable domain entity Persistence.swift
@ModelActor for background work, converting to value types inside Persistence.swift
PersistentIdentifier crosses the actor boundary; the model never does Persistence.swift
One ModelContainer, owned by the composition root Persistence.swift
A push source behind an AsyncSequence protocol Streaming.swift
Streamed updates matched by identity, cancellation as a no-op ArticleListModel.consumeUpdates

The tests are the interesting part: several exist specifically to fail if a rule is violated. testToggleBookmarkRevertsOnFailure fails if the revert uses a stale index. testCancellationIsNotReportedAsError fails if CancellationError is treated as user-facing. testLinkBeforeReadyIsQueuedThenFlushed fails if a launch-time deep link is dropped. testImportIsIdempotent fails if the upsert degrades into a blind insert, which the @Attribute(.unique) constraint only punishes later, at save time. testTheSameViewModelDrivesSwiftDataUnchanged fails if the boundary protocols were decorative — it runs the same ArticleListModel over a real ModelContainer with nothing changed.

Timing-sensitive transitions go through Gate (Streaming.swift), which makes the suspension deterministic. Tests that sleep and hope pass locally and flake in CI, which is worse than no test: they teach people to re-run until green.

Scope

Deliberately limited to stable APIs — iOS 17 / macOS 14, no SwiftUI view code, no beta SDKs — so it builds on standard CI runners with swift build and no simulator. SwiftData qualifies: it shipped in iOS 17, and every container here is isStoredInMemoryOnly, so the suite needs no disk and leaves nothing behind.

Consequences, stated plainly:

  • Compile-checked: architecture, isolation, concurrency, routing, DI, error handling.
  • Not compile-checked: SwiftUI view bodies, Liquid Glass, Foundation Models, and anything else needing a beta SDK or a UI framework. Those docs carry a verification note for exactly this reason.

Strict concurrency is enabled in Package.swift, so an isolation regression fails the build rather than shipping.

Adding to it

A pattern belongs here once it is (a) stable-API, (b) expressible without SwiftUI view code, and (c) testable in a way that fails when the rule is broken. A test that passes whether or not the pattern is followed adds nothing.