r3-reactive-extensions

R3: Modern Reactive Extensions for .NET

R3 is Cysharp's ground-up reimplementation of Reactive Extensions — "the new future of dotnet/reactive and UniRx." It keeps the LINQ-over-events programming model but rebuilds the core types, error contract, and scheduler to fix long-standing problems in System.Reactive (Rx.NET). Use this skill when composing event streams, UI input, timers, or push-based pipelines in C#.

Canonical sources (link to these from code and docs):

• Repository: https://github.com/Cysharp/R3
• README (full operator reference): https://github.com/Cysharp/R3/blob/main/README.md
• Author's design rationale: https://neuecc.medium.com/r3-a-new-modern-reimplementation-of-reactive-extensions-for-c-cf29abcc5826

When to Use This Skill

Use this skill when:

• Composing events over time — UI input, sensor/feed updates, websocket messages, domain events
• You need operators like debounce, throttle, merge, combine-latest, distinct-until-changed
• Building MVVM state with ReactiveProperty / BindableReactiveProperty
• Bridging push-based streams with Task / async and IAsyncEnumerable
• Migrating from System.Reactive, UniRx, or IObservable<T> code
• You hit Rx pain points: subscriptions dying on exceptions, scheduler overhead, or leak hunting

Not the right tool for: request/response I/O (use async/await), bounded producer/consumer with backpressure (use System.Threading.Channels), or server-side stream processing with batching/backpressure (use Akka.NET Streams). R3, like all Rx, is push-based with no backpressure. See the csharp-concurrency-patterns skill for choosing between these.

Reference Files

• rx-net-differences.md: Every meaningful difference vs System.Reactive (Rx.NET) — the new core types, the error model, operator renames, dropped APIs, the scheduler swap, and a migration checklist.
• async-and-integration-patterns.md: Common patterns — async dispatch with AwaitOperation, Task integration, IAsyncEnumerable round-tripping, ReactiveProperty/MVVM, subjects, and subscription lifecycle.
• scheduling-and-concurrency.md: How R3 handles concurrent updates (the threading contract, Synchronize, ObserveOn), TimeProvider vs FrameProvider, when each is necessary, and deterministic testing with fake providers.