Cold signals in ReactiveCocoa emit a complete, independent sequence for each subscriber only after subscription, while hot signals continuously push shared events regardless of listeners, causing later subscribers to miss earlier values; understanding this distinction guides proper signal choice in FRP applications.
Understanding ReactiveCocoa’s cold and hot signals reveals that each subscription to a cold fetchData signal triggers a separate network request, causing duplicated calls, while converting the signal to hot with shareReplay or publish ensures a single request is shared across UI bindings and error handling.
The article explains that in ReactiveCocoa cold signals are plain RACSignal instances that start their work per subscriber, while hot signals are RACSubject (or subclasses) that broadcast a single execution to all observers, and demonstrates converting cold to hot using subjects, multicast operators, and replay helpers such as replayLazily to share network requests.
