reactivex/rxswift

RxSwift is a Swift library that brings Reactive Programming to iOS, macOS, tvOS, and watchOS development. Reactive programming is a coding style where you treat data as a continuous stream of values over time, like a river of events, and write code that automatically responds to changes in that stream rather than manually wiring up callbacks and state tracking. In practical terms, RxSwift lets you describe complex event-driven behaviors (like: "when the user types in a search box, wait 300 milliseconds, then fetch results from the network and display them in the table view") as a clean, readable pipeline of transformations instead of a tangle of delegates, callbacks, and state variables. The core building block is an Observable, a source of values that other parts of your code can subscribe to and react to. The library includes several components: the core RxSwift framework, RxCocoa (which adds iOS and macOS UI bindings so you can directly connect UI elements like buttons and text fields to observable streams), RxRelay (simple wrappers for sharing state), and RxTest/RxBlocking (for unit testing reactive code). iOS and macOS developers use RxSwift when building apps that need to handle lots of asynchronous events, network calls, user input, timers, and want a more structured and composable approach than traditional imperative coding. It is the Swift implementation of the broader ReactiveX standard, which has versions for many other languages.