An Introduction to Reactive Extensions. Demo Code available at http://github.com/james-world/rxtalk. Note: Most of these slides were willfully plagiarised from slides and bits of demos done by the Rx-Team themselves, and repurposed to fit into a 20 minute datablast! Special thanks to the awesome Erik Meijer and Bart de Smet whose permission I didn't seek... I hope they don't mind!

1. a brief introduction to
Reactive Extensions
JAMES WORLD

2. A library for the composition of asynchronous and
event-based programs using observable
sequences and LINQ-style operators.

3. interactive streams
public interface IEnumerable<out T> : IEnumerable
{
IEnumerator<T> GetEnumerator();
}
public interface IEnumerator<out T> : IDisposable, IEnumerator
{
bool MoveNext();
T Current { get; }
void Reset();
}

4. composability
var openOrders =
from customer in context.Customers
from order in customer.Orders
where customer.CustomerId == 101
where order.Status == OrderStatus.Open
select order;

5. composability
var openOrders = context
.Customers
.Where(c => c.CustomerId == 101)
.SelectMany(c => c.Orders)
.Where(o => o.Status == OrderStatus.Open);

6. reactive streams
public interface IObservable<out T>
{
IDisposable Subscribe(IObserver<T> observer);
}
public interface IObserver<in T>
{
void OnNext(T value);
void OnError(Exception error);
void OnCompleted();
}

7. OnNext OnError OnCompleted

8. creating observables
Observable.Return(42);
Observable.Never<int>();
Observable.Empty<int>();
Observable.Throw<int>(Exception error);
Observable.Timer(TimeSpan delay);
Observable.Interval(TimeSpan period);
Observable.Generate(…);
Observable.Create(…);

9. Social
media
RSS feeds
GPS
Server management

10. if “MSFT”
// Imperative code
/* what goes here? */

11. IObservable Quote
var
“MSFT”
var /* … */

12. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
from tick in ticks

13. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
27.01 27.96 31.21 30.73
21.75 22.54 20.98
from tick in ticks
group tick by tick.Symbol

14. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
from tick in ticks
group tick by tick.Symbol into company
from openClose in company.Buffer(2, 1)
[27.01, 27.96] [27.96, 31.21] [31.21, 30.73]
[21.75, 22.54] [22.54, 20.98]

15. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
from tick in ticks
group tick by tick.Symbol into company
from openClose in company.Buffer(2, 1)
let diff = (openClose[1] – openClose[0]) / openClose[0]
0.034 0.104 -0.015
0.036 -0.069

16. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
from tick in ticks
group tick by tick.Symbol into company
from openClose in company.Buffer(2, 1)
let diff = (openClose[1] – openClose[0]) / openClose[0]
where diff > 0.1
0.034 0.104 -0.015
0.036 -0.069

17. MSFT
27.01
INTC
21.75
MSFT
27.96
MSFT
31.21
INTC
22.54
INTC
20.98
MSFT
30.73
from tick in ticks
group tick by tick.Symbol into company
from openClose in company.Buffer(2, 1)
let diff = (openClose[1] – openClose[0]) / openClose[0]
where diff > 0.1
select new { Company = company.Key, Increase = diff }
Company = MSFT
Increase = 0.104

18. schedulers parameterize concurrency
IObservable long TimeSpan
IScheduler scheduler

19. var Observable.Return Scheduler.ThreadPool
"Answer = "
xs.ObserveOn(new ControlScheduler(frm))
.Subscribe(x => lbl.Text = "Answer = " + x);
xs.ObserveOn( frm )
.Subscribe(x => lbl.Text = "Answer = " + x);

20. async Task<string> GetHtmlAsync(Uri url)
{
var client = new WebClient();
var download = client.DownloadStringAsync(url);
var timeout = Task.Delay(TimeSpan.FromSeconds(30));
if (await Task.WhenAny(download, timeout) == timeout)
throw new TimeoutException();
var html = await download;
return html;
}
async without Rx

21. async Task<string> GetHtmlAsync(Uri url)
{
var client = new WebClient();
var download = client.DownloadStringAsync(url)
.ToObservable()
.Timeout(TimeSpan.FromSeconds(30));
var html = await download;
return html;
}
async with Rx

22. demo

23. @jamesw0rldlinkd.in/james-world
reactivex.io
www.introtorx.com
stackoverflow.com
rx-main rx-xaml rx-testing