johnrogers/composable-architecture

The Composable Architecture (TCA)

TCA provides architecture for building complex, testable features through composable reducers, centralized state management, and side effect handling. The core principle: predictable state evolution with clear dependencies and testable effects.

Reference Loading Guide

ALWAYS load reference files if there is even a small chance the content may be required. It's better to have the context than to miss a pattern or make a mistake.

| Reference | Load When | |-----------|-----------| | Reducer Structure | Creating new reducers, setting up @Reducer, State, Action, or @ViewAction | | Views - Binding | Using @Bindable, two-way bindings, store.send(), or .onAppear/.task | | Views - Composition | Using ForEach with stores, scoping to child features, or optional children | | Navigation - Basics | Setting up NavigationStack, path reducers, pushing/popping, or programmatic dismiss | | Navigation - Advanced | Deep linking, recursive navigation, or combining NavigationStack with sheets | | Shared State | Using @Shared, .appStorage, .withLock, or sharing state between features | | Dependencies | Creating @DependencyClient, using @Dependency, or setting up test dependencies | | Effects | Using .run, .send, .merge, timers, effect cancellation, or async work | | Presentation | Using @Presents, AlertState, sheets, popovers, or the Destination pattern | | Testing - Fundamentals | Setting up test suites, makeStore helpers, or understanding Equatable requirements | | Testing - Patterns | Testing actions, state changes, dependencies, errors, or presentations | | Testing - Advanced | Using TestClock, keypath matching, exhaustivity = .off, or time-based tests | | Testing - Utilities | Test data factories, LockIsolated, ConfirmationDialogState testing, or @Shared testing | | Performance | Optimizing state updates, high-frequency actions, memory, or store scoping |

Common Mistakes

1. Over-modularizing features — Breaking features into too many small reducers makes state management harder and adds composition overhead. Keep related state and actions together unless there's genuine reuse.

2. Mismanaging effect lifetimes — Forgetting to cancel effects when state changes leads to stale data, duplicate requests, or race conditions. Use .concatenate for sequential effects and .cancel when appropriate.

3. Navigation state in wrong places — Putting navigation state in child reducers instead of parent causes unnecessary view reloads and state inconsistencies. Navigation state belongs in the feature that owns the navigation structure.

4. Testing without TestStore exhaustivity — Skipping TestStore assertions for "simple" effects or "obvious" state changes means you miss bugs. Use exhaustivity checking religiously; it catches regressions early.

5. Mixing async/await with Effects incorrectly — Converting async/await to .run effects without proper cancellation or error handling loses isolation guarantees. Wrap async operations carefully in .run with yield statements.