RxSwift

RxSwift is a library for composing asynchronous and event-based programs by using observable sequences for the Swift programming language. It is a port of ReactiveX's Reactive Extensions and provides a consistent API for working with streams of data and events. Developers can create observables from arrays, network responses, user actions, or timers, and compose them with operators to transform, filter, combine, and react to data flows.

The core concepts include Observables, which emit events; Observers (subscribers) that receive events; and a family of operators that transform and compose streams. Subjects act as both observers and observables and can multicast to multiple subscribers. RxCocoa adds UI bindings for Cocoa and Cocoa Touch components, enabling reactive bindings for controls, text fields, and gesture handling.

Subscriptions have lifecycles managed via Disposable objects and DisposeBag, which automatically cancel subscriptions when deallocated. Scheduling primitives (schedulers) control where and when work is executed, with MainScheduler for UI work and various background schedulers for asynchronous tasks. RxSwift emphasizes declarative programming and predictable error handling by propagating errors through the data stream.

RxSwift is widely used in iOS and macOS development to coordinate asynchronous operations, network requests, animations, and user input without nested callbacks. It benefits from a large operator ecosystem and interoperability with other ReactiveX libraries, especially via RxCocoa for UI bindings. It is open-source and community-maintained, with development and discussions hosted on public repositories.