The document outlines the concept of reactive programming and the Reactive Extensions (Rx) library, which allows for composing asynchronous data streams using observable sequences. It discusses various components of Rx, such as operators for creating, transforming, filtering, and combining observables, as well as its application across multiple programming languages. Additionally, it highlights practical use cases and examples demonstrating the benefits of using Rx in building responsive applications.

1. MAXIME LEMAITRE – 23/12/2015
Reactive Extensions
buzzs.Filter(IsAwesome).Subscribe(s=> {levelup++;})

2. Agenda
• Introduction
• Reactive Programming
• Reactive Extensions
• Rx.Net
• Examples
• Question
Reactive Extensions aka Rx,
origninally Crafted by
Microsoft in 2009

3. What is Reactive Programming ?
Reactive programming is programming of
asynchonous data streams.
More definitions : Wikipedia, Stackoverflow, Reactive Manifesto, Microsoft
A responsive application is the goal.
A responsive application is both
scalable and resilient. Responsiveness is
impossible to achieve without both scalability
and resilience.
A message-driven architecture is the
foundation of scalable, resilient, and ultimately
responsive systems.

4. What is a Stream ?
• A Stream is a Sequence of items in a particular order that may or may
not end
• It can emit three different things:
– a value (of some type),
– an error
– "completed" signal.
All these events can be
asynchronous
• A list/collection can be seen as a
stream
– Determinist
– Ended

5. Streams are everywhere
anything can be a stream:
events, variables, user inputs,
properties, caches, data
structures, etc.

6. What are Reactive Extensions (Rx)?
• The Reactive Extensions (Rx) is a library for composing asynchronous and event-
based programs using observable sequences and LINQ-style query operators.
• It provides a collection of operators with which you can filter, select, transform,
combine, and compose Observables. This allows for efficient execution and
composition.
• From Pull Model => Iterable (Iterator Pattern) to Push Model => Observable
(Observer Pattern)

7. Pull vs Push Models

8. Better codebases

9. Rx is everywhere
• Rx is available in most programming languages
– Java: RxJava
– JavaScript: RxJS
– C#: Rx.NET
– C#(Unity): UniRx
– Scala: RxScala
– Clojure: RxClojure
– C++: RxCpp
– Ruby: Rx.rb
– Python: RxPY
– Groovy: RxGroovy
– JRuby: RxJRuby
– Kotlin: RxKotlin
– Swift: RxSwift
“The desktop developers at
GitHub loved Rx so much, that
the Mac team created their own
version of Rx and ReactiveUI,
called ReactiveCocoa, and are
now using it on the Mac to
obtain similar benefits.” – Paul
Betts, GitHub

10. Rx Operators• Creating Observables
– Create, Defer, Empty/Never/Throw, From , Interval, Just, Range, Repeat, Start, Timer
• Transforming Observables
– Buffer, FlatMap, GroupBy, Map, Scan, Window
• Filtering Observables
– Debounce, Distinct, ElementAt, Filter, First, IgnoreElements, Last, Sample, Skip, SkipLast, Take,
TakeLast
• Combining Observables
– And/Then/When, CombineLatest, Join, Merge, StartWith, Switch, Zip
• Error Handling Operators
– Catch, Retry
• Observable Utility Operators
– Delay, Do, Materialize/Dematerialize, ObserveOn, Serialize, Subscribe, SubscribeOn,
TimeInterval, Timeout, Timestamp, Using
• Conditional and Boolean Operators
– All, Amb, Contains, DefaultIfEmpty, SequenceEqual, SkipUntil, SkipWhile, TakeUntil, TakeWhile
• Mathematical and Aggregate Operators
– Average, Concat, Count, Max, Min, Reduce, Sum
• Connectable Observable Operators, …

11. Understand Operators with Marble Diagrams
http://rxmarbles.com/

12. Rx.Net
Rx is …
1. a set of types representing asynchronous data streams
2. a set of operators to query asynchronous data streams
3. a set of types to parameterize concurrency
Rx = Observables + LINQ + Schedulers

13. IObservable, IObserver
Part of .NET 4

14. How to create observables in Rx.Net ?
• Factory Methods
– Observable.Return
– Observable.Empty
– Observable.Never
– Observable.Throw
– Observable.Create
• Unfold methods
– Observable.Range
– Observable.Interval
– Observable.Timer
– Observable.Generate
• Paradigm Transition
– Observable.Start
– Observable.FromEventPattern
– Task.ToObservable
– Task<T>.ToObservable
– IEnumerable<T>.ToObservable
– Observable.FromAsyncPattern

15. Example #1 : Event Processing
Given: Stream of stock ticks
Find: 10% daily price increase

16. Example #1 : Event Processing
from tick in stockTicks
group tick by tick.Symbol into symbolStream
from window in symbolStream.Buffer(2, 1)
let increase = PriceIncrease(window)
where increase > .1
select new { symbol = symbolStream.Key, increase };

17. Use case #2 : AutoComplete TextBox (RxJs)
Common Problems : Too many requests on the servers, bad user experience, sluggy
animations, error handling, duplicated requests …

18. Use case #2 : AutoComplete TextBox (RxJs)
Full code https://github.com/Reactive-Extensions/RxJS/tree/master/examples/autocomplete
1 – Search function
3 – Subscribe
2 – Composition

19. Example#3 : Monitoring
• Day 0 
– 1 Client
– Used for one features
• Day N 
– X Clients (X >>1)
– Used everywhere
– New features on API side
incr Hit
Update Node
Update Metrics
a few commands/min
a few 10 000s/secs

20. Example#3 : Monitoring
• Basic idea : Buffer commands increment Hit every 5 secs
Update Node every 500 hits
Update Metrics once/minute

21. Quizz
• What’s the difference between Rx and
databinding ?
• Should I have to use Rx since .net 4.5
(await/async) ?
• Where is Rx appropriate ?
• Should I have to create my own
observables/observers ?
• How do manage UI/main
thread/multithreading with ReactiveX ?
• ….

22. Questions

23. References
• https://gist.github.com/staltz/868e7e9bc2a7b8c1f754
• http://www.introtorx.com/
• http://reactivex.io/
• https://github.com/Reactive-Extensions
• https://blog.xamarin.com/why-every-mobile-developer-should-use-reactive-programming/
• https://vimeo.com/43659034
• https://github.com/kriskowal/gtor
• https://www.youtube.com/watch?v=5DZ8nC0ENdg
• http://futurice.com/blog/reactive-c-number-in-practice
• http://rxwiki.wikidot.com/101samples
• https://medium.com/reactive-programming/what-is-reactive-programming-bc9fa7f4a7fc#.x0tnt96i4

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