pointfreeco/swift-composable-architecture

The Composable Architecture, shortened to TCA in the README, is a Swift library for structuring apps that run on Apple platforms. The README lists iOS, macOS, iPadOS, visionOS, tvOS, and watchOS as supported, and says the library works with both SwiftUI and UIKit, the two main user-interface toolkits Apple developers choose between. The pitch is that it gives a consistent shape for an app's code so that the same patterns work whether the screen is tiny, like a watch face, or large, like a Mac window. The README breaks the problem the library is solving into five themes. State management is about keeping a single source of truth for the data a feature needs, with that data shared across screens so that a change in one place shows up everywhere. Composition is about splitting a big feature into smaller pieces that can live in their own modules and be plugged back together. Side effects covers anything that talks to the outside world, like network calls, in a way that stays testable. Testing covers writing unit, integration, and end-to-end tests for features built with the library. Ergonomics is about doing all of the above with as few moving parts as possible. To build one feature, the README says you define four things. State is a type holding the data the feature works with. Action is a type listing everything that can happen, from a button press to a network reply. Reducer is a function describing how the current state turns into the next state given an action, and what side effects should run. Store is the runtime that wires these together: actions are sent into the store, the reducer processes them, effects execute, and the UI observes state changes. The README walks through a small example: a counter screen with plus and minus buttons and a third button that fetches a random fact about the current number from an API. It shows a struct annotated with the @Reducer macro, a State with a count integer and an optional number fact string, an Action enum listing the three button taps plus a separate case for the API response, and a body property that switches on the action and updates state or returns no effect. The library grew out of an episode series on Point-Free, a paid video site about advanced Swift programming run by Brandon Williams and Stephen Celis. The repository ships many example apps including a search demo, speech recognition, voice memos, todos, and tic-tac-toe, along with case studies covering navigation, effects, and reusable components. A bigger example is isowords, an iOS word game whose source is open.