# Composable Architecture > Use when building features with TCA (The Composable Architecture), structuring reducers, managing state, handling effects, navigation, or testing TCA features. Covers @Reducer, Store, Effect, TestStore, reducer composition, and TCA patterns. - Skill: `tomevault-io/composable-architecture` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/composable-architecture` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/composable-architecture/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/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. ## Overview - **[Reducer Structure](references/reducer-structure.md)** - Templates, @Reducer, State, Actions, @ViewAction, conformances - **[Views](references/views.md)** - StoreOf, @Bindable, ForEach, store.scope, view actions - **[Navigation](references/navigation.md)** - NavigationStack, StackState, path reducers, dismiss - **[Shared State](references/shared-state.md)** - @Shared, .appStorage, .withLock, FileStorageKey, InMemoryKey - **[Dependencies](references/dependencies.md)** - @DependencyClient, @Dependency, DependencyKey, streaming - **[Effects](references/effects.md)** - .run, .send, .merge, catch:, timers, cancellation - **[Presentation](references/presentation.md)** - @Presents, Scope, AlertState, multiple destinations - **[Testing](references/testing.md)** - TestStore, TestClock, exhaustivity, dependency mocking - **[Performance](references/performance.md)** - Optimization, high-frequency updates, memory ## 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. --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/goodevibes) — claim your Tome and manage your conversions.