A Brief Introduction To Reactive Extensions

a brief introduction to
Reactive Extensions
JAMES WORLD

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

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();
}

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

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

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();
}

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(…);

Social
media
RSS feeds
GPS
Server management

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

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

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

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

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]

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
let diff = (openClose[1] – openClose[0]) / openClose[0]
0.034 0.104 -0.015
0.036 -0.069

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
where diff > 0.1
0.034 0.104 -0.015
0.036 -0.069

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
where diff > 0.1
select new { Company = company.Key, Increase = diff }
Company = MSFT
Increase = 0.104

schedulers parameterize concurrency
IObservable long TimeSpan
IScheduler scheduler

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);

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

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

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

A Brief Introduction To Reactive Extensions

A Brief Introduction To Reactive Extensions

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