Reactive Extensions (Rx)

A quick overview of the concepts behind Reactive Extensions. I also briefly touch on Reactive Cocoa and show some basic examples

1. Reactive Extensions (Rx) Ray Hilton @rayh Friday, 14 December 12
2. a form of FRP (Functional Reactive Programming) Friday, 14 December 12
3. a = b + c Friday, 14 December 12
4. Imperative Programming • evaluation occurs at time of assignment • if the values of b or c later change, a remains unaffected Friday, 14 December 12
5. FRP • a is /bound/ to the result of b + c • Consequent changes to b or c will re- evaluate b + c and assign the result to a • Formulas in spreadsheets are a good example • Obj-C KVO can be used in this way Friday, 14 December 12
6. Subscribing to future states Friday, 14 December 12
7. Rx “a library for composing asynchronous and event- based programs using observable collections” Friday, 14 December 12
8. .NET Friday, 14 December 12
9. Async Events • Simplify asynchronous and event-based programming • Maximize concurrency but minimize explicit concurrency code • Avoid doing Too Much on the main thread • Scale across multiple cores Friday, 14 December 12
10. Composition • Sequence a series of simple async operators • Combine result of multiple async events • Avoid boiler plate code, keep intent clear Friday, 14 December 12
11. Observable Collections • Collections are async data sources that follow the Observer pattern • Scalar properties can thought of as a collection of values through time • .NET has LINQ, an SQL-like expression syntax for querying arbitrary data structures • filters, projections, joins and time-based operations Friday, 14 December 12
12. Operators • Filter and transform data as it flows through • Synonymous to IO stream programming • Chain many operations to only get the information you want • e.g. DistinctUntilChanged, Until/WaitUntil, Throttle(timeout) Friday, 14 December 12
13. Reactive Cocoa by GitHub Friday, 14 December 12
14. Simple examples ! [RACAble(self.text) subscribeNext:^(id x) { ! ! NSLog(@"text: %@", x); ! }]; ! [[RACAble(self.text) ! ! map:^(id x) { ! ! ! return [x uppercaseString]; ! ! }] ! ! toProperty:@keypath(self.label) onObject:self]; ! [self rac_bind:@keypath(self.text) to:self.view.textField.rac_textSignal]; Friday, 14 December 12
15. Async Image Loading ! [[[[[RACAble(self.userAccount.avatarURL) ! ! filter:^ BOOL (id x) { ! ! ! return x != nil; ! ! }] ! ! deliverOn:[RACScheduler scheduler]] ! ! flattenMap:^(NSURL *URL) { ! ! ! return [UIImage imageWithContentsOfURL:URL]; ! ! }] deliverOn:RACScheduler.mainThreadScheduler] subscribeNext:^(id image) { self.imageView.image = image; }]; Friday, 14 December 12
16. Join Async Operations ! [[[RACSignal ! ! merge:@[[self fetchUser], [self fetchRepos]]] ! ! finally:^{ ! ! ! self.loading = NO; ! ! }] ! ! subscribeNext:^(id x) { ! ! ! NSLog(@"completed!”); ! ! } error:^(NSError *error) { ! ! ! NSLog(@"error: %@", error); ! ! } completed:^{ ! ! ! NSLog(@"done"); ! ! }]; Friday, 14 December 12
17. Conclusions • You are probably doings some of these things • Formalizes an approach for async event- based functional programming • Controllers become more declarative • Bracket notation kinda sucks for chaining many calls Friday, 14 December 12
18. Thanks Ray Hilton ray@wirestorm.net @rayh Friday, 14 December 12