Programming C# 8.0

Chapter 11. Reactive Extensions

The Reactive Extensions for .NET, or Rx, are designed for working with asynchronous and event-based sources of information. Rx provides services that help you orchestrate and synchronize the way your code reacts to data from these kinds of sources. We already saw how to define and subscribe to events in Chapter 9, but Rx offers much more than these basic features. It provides an abstraction for event sources that has a steeper learning curve than events, but it comes with a powerful set of operators that makes it far easier to combine and manage multiple streams of events than is possible with the free-for-all that delegates and .NET events provide.

Rx’s fundamental abstraction, IObservable<T>, represents a sequence of items, and its operators are defined as extension methods for this interface. This might sound a lot like LINQ to Objects, and there are similarities—not only does IObservable<T> have a lot in common with IEnumerable<T>, but Rx also supports almost all of the standard LINQ operators. If you are familiar with LINQ to Objects, you will also feel at home with Rx. The difference is that in Rx, sequences are less passive. Unlike IEnumerable<T>, Rx sources do not wait to be asked for their items, nor can the consumer of an Rx source demand to be given the next item. Instead, Rx uses a push model in which the source notifies its recipients when items are available.

For example, if you’re writing an application that deals with live financial ...