An Introduction to the Reactive Extensions Ivan Towlson Mindscape

Composable operators for working with sets of data Reintroducing LINQ

IEnumerable: the little interface that could

Extends IEnumerable to support translation of LINQ queries for processing by another engine IQueryable: the little interface that takes twelve years to implement

IEnumerable is a pull model Unpredictable streams are better handled by a push model Pulling and pushing

Introducing IObservable

interface IEnumerable { IEnumerator GetEnumerator(); } interface IObservable { IDisposable Subscribe(IObserver ); }

interface IEnumerator { bool MoveNext(); T Current; } interface IObservable { void OnNext(T); void OnError(Exception); void OnCompleted(); }

An implementation of the LINQ standard query operators (and more) for the IObservable interface Introducing the Reactive Extensions

IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What?

A unified, declarative, composable way of working with asynchronous sources Builds on existing sources of asynchrony, rather than replacing them Introducing the Reactive Extensions

Like LINQ, Rx doesn’t do anything you couldn’t do in your own code, but it wraps up a lot of boilerplate and ad hoc code into convenient, composable operators Introducing the Reactive Extensions

Where does asynchronous data come from?

Events as asynchronous data

Revisiting the asynchronous method pair pattern

Not useful in themselves, but useful for composition Observable.Create: explicitly spelling out the event sequence (like an iterator) Primitive constructors and generators

The pulls push and the pushers pull with apologies to P J Harvey

IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What? ToXxx AsXxx

What can we do with asynchronous data once we’ve got a source?

Where Select / SelectMany Count / Any / All and all the rest LINQ operators

Scan Buffer (with time and count options) TakeUntil Merge / Amb And a whole lot more besides

Sample Throttle / Timeout Timestamp / TimeInterval DistinctUntilChanged And a whole lot more besides

What about timing? What about threading?

IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What? When? IScheduler

Immediate Thread pool, task pool WPF or WinForms UI thread Custom Schedulers

ObserveOn SubscribeOn Or we could just do it right here on the UI thread

Sorry, Visual Basic fans, but the doors are now locked A brief interlude for the obligatory eggheadtude

IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What? dual homoiconic

Orthogonality fail?

IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What? FILL ME

Also known as IQueryableObservable or IShouldntChooseNamesWhileStoned Introducing IQbservable

Allows queries to be translated for processing by external push sources Like IQueryable, filtering, aggregation, etc. can be performed at the source Introducing IQbservable

LINQ to * IEnumerable LINQ to Objects IObservable “LINQ to Events” IQueryable e.g LINQ to SQL Pull (interactive) Push (reactive) Translatable (expression trees) Fixed (MSIL) How? What? IQbservable e.g. LINQ to WMI

.NET, Silverlight: download from MSDN Windows Phone 7: included in ROM but can download updated version JavaScript: download from MSDN Availability

MSDN DevLabs – Projects > Rx PDC talk – FT10, Bart de Smet Rx Design Guidelines document Resources

Thanks! Ivan Towlson |