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.